I received my unlocked 4a today and moved my SIM from my other phone into the new phone and I can't access any of my voicemails. I'm on the phone with ATT tech support but I'm not very confident with the representative. How do I fix this?
Open your phone app, tap Menu>Settings>Voicemail>Advanced Settings>Setup, and make sure your voicemail number is your own 10 digit number. (For AT&T, to call into your voicemail, you have to dial your own number. It's different for other carriers like T-Mobile, which has a central voicemail number that's different from your own number.)