Members of the public should not be concerned about claims that they can be defrauded by hoaxers wanting to test their phone lines.
The warning, which according to BT spokesman Francis King resurfaces every few months, is in fact an urban myth.
It has been published in RSA News, the magazine for retired Marks and Spencers' employees.
It reads: "Members of the public are being caught out by hoax callers claiming to be AT&T service technicians conducting tests on the line.
"The hoaxer will ask you to press figures 9, 0, # on your phone and then hang up. The telephone company has confirmed that this will enable the hoaxer to make calls which will be billed to your phone.
"Under no circumstances should you take part in this test, it could cost you hundreds of pounds."
However, Mr King, said: "It's an urban myth which unfortunately keeps getting resurrected by well meaning bodies.
"There is no way BT customers can be defrauded in the circumstances described. There is no reason to be concerned."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article