# The Telecommunications (Open Network Provision) (Voice Telephony) Regulations 1998, Part 1


(a) Tone dialling or DTMF (dual-tone multifrequency operation)
i.e. the fixed public telephone system supports the use of DTMF telephones for signalling to the exchange, using tones as defined in ETSI ETR 207, and supports the same tones for end-to-end signalling throughout the system both within a Member State and between Member States.
(b) Selective call barring for outgoing calls
i.e. the facility whereby the subscriber can, on request to the telephone service provider, bar outgoing calls of defined types or to defined types of numbers.

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Source: https://www.legislation.gov.uk/uksi/1998/1580/schedule/I/part/1 (the official version)
Page: https://openlegislation.uk/telecommunications-open-network-provision-voice-telephony-regulations-1998/schedule-I/part-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.