If you're somewhat tech savy, or at least have some determination, I recommend using a monthly prepaid plan and using VoIP calls.
http://prepaid-phones.t-mobile.com/prepaid-plans (on the bottom left, 100 mins/unlimited text/unlimited calling)
http://forum.xda-developers.com/show....php?t=2057887
$30/month and some know how can get you unlimited everything. You can go a step further using FreedomPop and get completely free service, although you're limited to 500 mb/month until you start paying and it requires you to micromanage your WiFi connection if you want to optimize your data usage (too much hassle imo)