Visual Voicemail has disappeared-4s help iPhone

I have purchased a new iPhone 4s (white) with AT&T service. My wife picked up my previous iPhone 4 and activated it on her account.

The visual voicemail option on the iPhone 4s is not working. By pushing the voicemail button under phone, then bottom right, it dials my voicemail the old-fashioned way, without ever appearing on the screen with visual voicemail options. Once the call is dialed, I can check my voicemail as if I were calling it from another phone by entering my password and progressing through the touch tone options. My original voicemail and greeting is the same as it was before I purchased the new phone, but the only way to change the greeting is under the personal options selection of the manual dial.

Visual voicemail is working fine for my wife's phone. I am on the phone with AT&T for the third time in less than 24 hours, checking options and resetting information. While I can still access voicemail, this was never the way it was intended to work.

Has anyone else experienced this issue and able to provide some assistance on what may be the problem? I am very proficient in using the iPhone visual voicemail - I have had every different iPhone device since the platform launched. But this is a very new problem for me and I have no way to fix it.

Thanks.