How To Fix AT&T iPhone Visual Voicemail Notification Alerts
One of the most frustrating and surprisingly under reported issues is with AT&T and iPhone Visual Voicemail notifications. When you receive a voicemail on your iPhone, an alert appears and you can play your voicemail as if its a song. There is now a solution!
Since the iPhone 3GS was released, some customers experienced lack of alerts for voicemail (me being one of them). I recently found a fix for it while I was researching tethering for 3GS. Apparently, tethering your iPhone may cause this issue.
So here’s the fix. Navigate to Settings → General → Network → Cellular Data Network and within the Visual Voicemail section add “acds.voicemail” into the APN field. Your visual voicemail will now work once again.
CAUTION: This fix does break the tethering. You can’t have voicemail notifications and Internet tethering work at the same time.
Via Apple Blog