Traveling With iPhone on Robbers

[BuddhistGirafe]

Ok. So I am going away to the States for a week and I need to have my phone. Only problem is Robbers has TERRIBLE ROAMING charges. TERRIBLE. I recently switched from Bell to get the iPhone and on Bell I was comforted to free texting while roaming included in my unlimited texting plan. Now I need some help. I just unlocked my 3GS for this trip in order to possibly throw a Prepaid SIM in there. All I need is SMS. I just need to know how that works with a pre-paid SIM and what I should get. I heard you can pick them up at any 7/11 but I still need to know what to get. Anyone who has some expertise in this field and could help me would be awesome.