Hello! I am an international student preparing my Graduate Study in the US. I've got an Iphone which is unlocked, meaning that I don't need to insert the AT&T SIM card, neither do I need to sign a contract with AT&T to comply with its rate plan, right? So which company( SIM card) do you recommend to use? My demand for the 3G network is pretty much (better 1GB/month or above), but prices would better be $50 or below, thx!