What I've found so far is the card in TracFone and others will not work in any other GSM phone so far. I don't remember what others I tried so be specific so folk can tell you yes or no.
So far, I have yet to see folk take one of those cheap GSM pre-paid phones and put the card into some smart phone and make a call.
I currently have a contract w/AT&T that will exprire in Dec. I want to get a smartphone now but obviously I can't upgrade. My husband suggested that I go ahead and purchase the phone so when my contract is up I won't be tied to AT&T for another 2 years. I think that is a good idea b/c as I was looking around at plans I think a prepaid plan would be best for me as I don't really use my phone that much (I have over 2K rollover minutes in the bank). So I need a phone that I can buy now that will work with my existing AT&T contract but will be able to use at a later date for a prepaid plan when my contract comes up AND the prepaid plan may not neessarily be w/AT&T.