Hello, I got 3G 8GB iPhone as a birthday present. The iPhone has been officially purchased in Russia and already unlocked but doesn't have SIM card. I am currently live in US and my current provider is Sprint. Is it possible to find an alternative plan (At&T is too expensive) and purchase plan with GSM card from cheapest providers. I am looking for something under 50$ per month with voice and 3G data service. Any advice? Thanks!