Calling Line Identification
& Calling Number Display

Last Updated: 6 Sep 2004


Calling Line Identification


Calling Line Identification ("CLI") is a telephone network signalling capacity that generates data, at the time a telephone call is established, that identifies the calling party telephone number/s (i.e. the billing telephone number and in some instances also other numbers, such as an extension number in an office).

CLI is transmitted within the telephone network and has been for many years. In older telephone networks, it was often referred to as "ANI" (Automatic Number Identification). Among other things, CLI enables telephone companies to identify the telephone account to be billed for the cost of a call, for example, pre-selected long distance call carriers can identify their customer from CLI information.

CLI based services

In more recent years, a range of CLI based services have been developed using the telephone network signalling capacity. CLI is transmitted only within the telephone network, but CLI based services are taken past the network into the customer access network or 'local loop', using software installed in the telephone exchanges.

CLI based services are products that package the calling party number information (and sometimes also other information) in various ways so that telephone companies can sell, or freely provide, the caller's telephone number to the called party. Calling Number Display is an example of a CLI based service.

Up ArrowGo to Contents List

Calling Number Display

Calling Number Display ("CND") is a CLI based service that displays or presents the caller's telephone number to the recipient of the call (i.e. to the called party).

The called party's telephone answering equipment may receive the calling party's number in various ways including: in the form of information that is displayed on a telephone or computer screen, or automatically recorded in a database, or as an audio message, etc.

Calling Number Display and other CLI based services became available in Australia in late 1997.

CND is sometimes referred to as "Caller ID" or "Caller Identification". However, these terms are highly misleading. The information does not identify the caller, it identifies the telephone number from which someone is making a particular telephone call.

Up ArrowGo to Contents List


Privacy Issues and Risks

The privacy issues and risks posed by Calling Number Display Services have long been recognised in Australia. As the AUSTEL Privacy Advisory Committee remarked in 1995, when issuing privacy guidelines for the introduction of CND Services in Australia:

"CND offers the ability to deduce from the telephone number information which the individual may not have otherwise volunteered to the called party, whether by way of reference to other information sources, or the context or the call itself. For example the town or suburb of a caller can be readily inferred from a phone number. Even more precisely, CND used in conjunction with reverse directories can establish the address of the calling telephone service by reference to the displayed phone number. In addition, the placement of calls to particular organisations, such as retailers, medical centres, or crisis lines, may carry inferences about the caller. The privacy implications of these uses of CND can be compounded in circumstances where organisational receivers do not institute appropriate identification verification procedures, and assume that the person making the call, and the customer whose name they have linked to the received phone number, are the same person." (Third Report of the AUSTEL Privacy Advisory Committee, 11 June 1998)
and as stated in the ACIF Industry Code:
"[Calling Number Display] raises some complex problems through the risks it poses to personal privacy, where it applies to existing telecommunications networks and participation is on an opt-out basis. Callers in many situations may not wish the receiver to be able to identify their telephone number. Doctors who call patients from home, customers who call businesses but do not wish to be contacted in the future, and victims of domestic violence are some of the groups who may not want their numbers disclosed. Integrated with other technologies, CND can allow increased collection and use of personal information, without the knowledge of the consumer." (ACIF Calling Number Display Industry Code C522)

Examples of how CND poses risks to personal privacy include:

  • Businesses can collect and use callers' numbers to build profiles about existing and prospective customers,
  • Business can use callers' numbers to discriminate against callers by delaying answering, or not answering, calls from particular numbers,
  • Call recipients can use callers' numbers to identify where the caller lives and/or works, who shares a residence with another person, whether the caller is away from home or work and where they are, etc.,
  • Businesses can use a prospective customer's telephone number to identify their address and send them unsolicited direct marketing material,
  • Call recipients may mistakenly match an anonymous caller's telephone number with the name of another person who makes calls from the same telephone number,
  • 'anonymous' enquiries to government departments and businesses may not be anonymous,
  • Internet Service Providers can include the CND blocking over-ride code in their automated connection/start up kits without telling their customers. This results in users' telephone numbers being transmitted to the ISP even when the user has a silent/unlisted telephone number or has instructed their telephone service provider to place a default block on CND transmissions from their telephone number.

Note: A number of the above practices would infringe Australian privacy protection laws and regulations depending on the circumstances in which, and by whom, such practices are undertaken and/or whether the caller has consented to the collection and use of their telephone number.

Privacy invasions:
Silent & Blocked Calling Number Disclosure to ISPs

If you have a silent (unlisted) telephone number, or have a Calling Number Display ("CND") block on your number, telephone companies may be over-riding your privacy choice when you or anyone else uses your telephone line to dial up an Internet Service Provider ("ISP") to log on to the Internet. Some, perhaps all, telephone companies commenced over-riding blocking in 2002 and 2003 on dial-up calls made to their ISP customers.

EFA believes the relevant telephone companies and ISPs are in breach of the law. For further information, see:

Up ArrowGo to Contents List

Legislation & Regulations re CND & CLI information


  • Telecommunications Act 1997 (C'th)
    Part 13 of the Act, titled "Protection of Communications", sets out strict rules that apply to all carriers, carriage service providers (including ISPs) and their employees in relation to their use and disclosure of personal information and communications that pass through their networks and creates criminal offences for non-compliance. In addition, Part 6 of the Act states the Parliament's intention that industry codes be developed and registered by the ACA, including codes in relation to privacy and calling number display (Section 112 and 113).
  • Privacy Act 1998 (C'th)
    Carriers and carriage service providers including ISPs are required to comply with the restrictions on collection, use and disclosure of personal information set out in the National Privacy Principles in the Privacy Act (unless the conditions of the small business exemption are applicable to them).

Privacy Conditions of Introduction of CND in Australia

CND services were introduced into Australia in December 1997 on the condition that callers must be able to prevent their telephone number being disclosed to the end-recipient of a call in order to protect the caller's privacy. In this regard, the Federal Government required telephone service providers to undertake to comply with privacy guidelines developed by the AUSTEL Privacy Advisory Committee ("PAC") in 1995. (AUSTEL was merged into the Australian Communications Authority in 1997).

The privacy guidelines included requirements that:

  • silent/unlisted numbers must have a permanent block implemented by the telephone service provider, unless the customer specifically requests otherwise;
  • other numbers could be displayed by default, but callers must be able to 'opt out' of disclosing their telephone number and must have the choice of a permanent, or a per call, block;
  • callers must be able to over-ride the default status of their line for a particular call by dialling a blocking or unblocking code before the telephone number (subsequently implemented as 1831 to block CND and 1832 to unblock CND); and
  • "line and per call blocking must be able to be implemented and be effective on all calls, including calls to Intelligent Network services (IN services) such as 1800 and 13 services".

The 'opt-out' basis (for numbers other than silent/unlisted numbers) was implemented despite widespread public criticism arising from the risks to personal privacy. Although a public education campaign was conducted, it was subject to significant criticism because, among other things, it failed to adequately warn the public about the privacy issues and risks. (Additional historical information about the introduction of CND in Australia is available later herein.)

The AUSTEL PAC privacy guidelines were subsequently incorporated, in 2000, into a Calling Number Display Industry Code of Practice that is enforceable by the Australian Communications Authority. Information about the Code is below.

Although the Australian public has been told since 1997 that telecommunications service providers are not permitted to over-ride caller choice blocking, except on calls to designated emergency services numbers (e.g. 000), in 2002 some telephone service providers started over-riding blocking on calls to other numbers without the caller's consent or even knowledge. For more information, see: Privacy invasions: Silent & Blocked Calling Number Disclosure to ISPs.

Industry Code

  • Calling Number Display Industry Code C522 (PDF 381Kb), Feb 2003, registered 25 June 2003.

    This Code, established under Section 112 of the Telecommunications Act 1997, is applicable to all telecommunications carriers and carriage service providers, including ISPs. It sets out enforceable rules for the operation of CND and restrictions on the use and disclosure of CND and Calling Line Identification ("CLI") information.

    The Code was developed by the Australian Communications Industry Forum ("ACIF") and registered by the Australian Communications Authority ("ACA") on 25 June 2003. (The Code replaces the previous Code registered on 30 October 2001, which had replaced an almost identical Code registered on 6 July 2000). The ACA is empowered by the Telecommunications Act 1997 to enforce compliance with registered Industry Codes. In addition the Telecommunications Industry Ombudsman is empowered to investigate complaints from individuals and small businesses concerning non-compliance with the Code.

    Among other things, the Code states:

    • "5.1.3 ... Suppliers [carriers and carriage service providers] (including ISPs) must not take steps to override a Caller's Permanent Line Block without the Caller's consent."
    • "7.1.3 Where a Supplier passes CLI information to an Organisational Customer, the Supplier must ensure it does not pass on its Customers full CLI information, except where required by Clause 5.3 [re emergency service numbers] or as otherwise permitted."
    • "5.8 No discrimination
      5.8.1 A Supplier [a carrier and a carriage service provider (includes an ISP)] must not unfairly discriminate between or offer different levels of service to Customers on the basis of whether those Customers choose CND or Blocking. (See note to Guideline 4 in Appendix A)."
      and that:
      "Examples of unfair discrimination include:
      - not servicing or providing a lesser service to Callers who choose not to display CND;"

Up ArrowGo to Contents List

Gov't and Industry Inquiries and Proposals


Review of the ACIF Calling Number Display Industry Code

Internet Industry Association ("IIA") efforts to force provision of CND to ISPs

In 2002, the Internet Industry Association of Australia ("IIA") commenced attempting to take away Internet users' existing rights to protect their privacy by blocking CND. As at mid 2003, these attempts have been partially successful, although as yet not all ISPs are receiving blocked calling number information. For more information see EFA's page: Privacy invasions: Blocked Calling Number Disclosure to ISPs.

NOIE recommendation re mandatory provision of CND to ISPs

Up ArrowGo to Contents List

Related Resources


Media Reports

  • See separate page on EFA's site for links to, and extracts from, media reports and releases concerning proposals to mandate Calling Number Display.

Historical information re introduction of CND in Australia

  • Telecommunications Privacy Report, Australian Telecommunications Authority (AUSTEL), Nov/Dec 1992
        A large part of this report discusses the privacy issues and risks associated with CLI and CND.
  • Calling Number Display - Third Report of the AUSTEL Privacy Advisory Committee, December 1995
  • [BROKEN LINK] Calling Number Display - Scoping Paper, Tim Dixon, Director, Australian Privacy Foundation, 4 Nov 1997
        Paper on the privacy issues surrounding the introduction of calling number display.
  • Safeguards on Calling Number Display, Media Release, Minister for Communications, the Information Economy and the Arts, Senator Richard Alston, 17 Nov 1997
        "Senator Alston said he had informed the three carriers of the Government's determination to see compliance with the safeguards recommended by the Privacy Advisory Committee (PAC) of the former telecommunications regulator AUSTEL...Senator Alston said he was requesting these measures on an interim basis pending the development by the Australian Communications Industry Forum (ACIF) of a code of practice on CND issues, which will be registered with the Australian Communications Authority."
  • Calling Number Display, Media Release, Minister for Communications, the Information Economy and the Arts, Senator Richard Alston, 19 Nov 1997
        "In the Senate today, Senator Natasha Stott Despoja asked what consumer safeguards would apply in relation to Calling Number Display (CND). As was made clear in a Government announcement earlier this week, the appropriate consumer safeguards are those contained in the Principles and Guidelines issued by AUSTEL in February 1996.
    The Government has made it clear to the carriers that they must comply with these safeguards."
  • Safeguards in place for start of CND trial on Monday, Media Release, Minister for Communications, the Information Economy and the Arts, Senator Richard Alston, 28 Nov 1997
        "The Minister...said today he was satisfied that safeguards were in place for the start of a trial of calling number display (CND) by Telstra in Adelaide on December 1. ...
    Telstra has also given the Minister a written commitment that it will make the CND Organisational Guidelines (developed by PAC) available to every business subscriber. As a condition of supply of the service, Telstra will reserve the right to withdraw the service from the subscriber subject to advice from an appropriate external authority regarding breaches of the Guidelines. The Australian Communications Authority (ACA) will act as the external authority. This will be an interim arrangement until a code on this matter is developed by the Australian Communications Industry Forum and registered by the ACA."
  • Telstra snubs CND Reference Panel, Australian Privacy Foundation Media Release, 29 Nov 1997
        Media release regarding the deferment of the implementation of CND in Australia.
  • Robyn Whittle's CND reference pages, 1997
  • More CND creases to be ironed out, Telecommunications Industry Ombudsman Media Statement, 13 Oct 1998
        "[T]he TIO regards it as a serious breach of privacy for [telephone service providers'] customer service operators to be using blocked CND information in their dealings with phone customers."

Up ArrowGo to Contents List