Letter: Your numbers are up

Sir: From Emma Jones's letter (19 December), and your Technology Correspondent's article ('Telecom says number is up for obscene phone callers', 17 December), there appears to be some confusion about the technology associated with identifying telephone callers.

Every call made by a subscriber in Britain carries its own identification which is why, when you call any of the service numbers (such as 100, 150 and 151), you no longer have to identify yourself as your details automatically appear on a VDU in front of the operator. It follows, therefore, that a simple 'caller display' system to attach to your own telephone could have been available a long time ago, and there is no valid reason why we should have to wait until 1994 for it.

However, there is no way individual subscribers could suppress their identification, because the ID signal carrier is an integral part of the digital exchange system.

Yours faithfully,

JAMES RUSBRIDGER

Lanivet, Cornwall