3gs old boot rom HELP!!

[nlang234]

I have a iphone 3gs from rogers i moved from canada and threw away my sim and got a 4s from sprint and now i want to use my 3gs as a ipod and it had 4.2.1 worked perfect and i upgraded to 5.0.1 and now i cant activate it i brought it to att best buy and apple and they did not fixed it please help