T-mobile has a $30 prepaid plan that looks pretty good (100 minutes talk, unlimited text and "unlimited" [throttled after 5gb] data).
http://prepaid-phones.t-mobile.com/prepaid-plans, click "Which plan is right for you?"
http://prepaid-phones.t-mobile.com/prepaid-plans, click "Which plan is right for you?"
http://www.metropcs.com/metro/detail/MetroPCS_SIM_Card/61021...
I usually stay under 100 minutes or go just up to the edge. If I'm at home and expect to be on hold or talk for a long time, I'll just use Google Voice from my computer, which is better than holding a phone anyway.
Plan #1: $30 for 100 minutes, with $0.10 a minute afterwards.
Plan #2: $40 for unlimited minutes with MetroPCS.
So, if I manage to talk less than 100min + ($50 - $40)/$0.10 = 200 minutes per month, then I end up spending less than I would on the MetroPCS plan.