If you're in the UK, I would go for a cheap PAYG contract, like that 3 deal and a cheap old Nokia or something that can be bought unlocked for less than 40 quid. You really don't need a more expensive phone if all you want it calls and texts, and some of them even do mapping.
However, judging by the OPs local time he's somewhere east coast US, and there I don't believe you can but a SIM and phone seperately, so you're more at the mercy of what operators will offer you. And USian members able to advise here?