Hi Ruker,
I am also on the old unlimited data plan (thankfully) and I downloaded the AT&T Visual Voicemail app from Google Play.
You might have to call 611 and have them add the visual voicemail configuration to your acct. There is no extra charge for this.
Good luck, let me know how it works out. By the way the app works great and it is not to be confused with AT&T's Messages app, thats a disaster.
