By pushing 90#, you give the requesting individual full access to your telephone line enabling them to place long distance calls billed to your home phone number.
Here is the Scam scenario:
You will receive a telephone call from an individual identifying himself as an AT&T Service technician conducting a test on telephone lines.
He stated that to complete the test you should touch nine(9), zero(0), the pound sign (#), and then hang up.
This scam has been originating from many local jails/prisons, and been confirmed by UCB Telecom,Pacific Bell, MCI, Bell Atlantic and GTE.