You call the dealer service dept, and give them your VIN. They look it up in Volvo's computer and you get the code. There may be a red and white card in your folder in the glovebox giving the original code.
Note that if the radio was ever replaced, it will have a different code, and it may be necessary to remove the stereo in order to read the serial number on top. It wouldn't need to be disconnected in this case.
Hopefully also the radio says "codE" on the display- if you enter the wrong code twice, the radio goes to "OFF" mode and requires a delay of about 2-4 hours before it will let you enter a code again.
These security codes are the most idiotic thing I've seen in car stereos. Who wants to steal a Volvo factory stereo anyway?
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Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K