I think I prefer the TMO deal since for $30 you get unlimited text, unlimited data and 100 minutes. The Sim cost $5. If you want to make lots of calls you can always use Vonage over 3g.
If you have a 850/2100 phone then this MVNO deal might be better since the direct ATT prepaid deals are not so good for data.
System One: Popcorn Hour A200, PS3 (US 60G) dead and now replaced with a PS3 SuperSlim, NPVR running on Sempron 3000 (XP), Sony BDP-S390 BD player, Logitech Revue, Pioneer AVR, JVC 56" D-ILA 720P RP TV
System Two: Popcorn Hour A110 , Oppo BDP-80 BluRay Player with hardware mode to be region free, Vivitek HD1080P 1080P DLP projector with 100" screen. Harman Kardon HK AVR 254 7.1 receiver, Toshiba HD-A2 HD-DVD player, Roku XS media player