I had set up a customer's phone system's voicemail to outdial to
Cingular/ATT Fort Worth number of 817-999-9302.

The autodial sequence is:
817-999-9302-pause-[cellphone number]-pause-5-pause-1

It still works for their ATT phones, but the manger upgraded
to an iPhone and the ATT VM no longer recognizes his number.
After you input the [cellphone number], is says its not a valid
number, but his iPhone can still call his VM.

Any clues?