ok so tell me if this will work? *my moms line on our family plan is eligible for an upgrade. (as i am not) shes gonna come with me and purchase the 3gs then when we leave we will swap phones and sim cards.* monday-i sell my original iphone 3g to my friend and take his ****** slide phone and put my sim in it for the week leading up to the 3g s launch friday-wait in line with my mother purchase iphone 3gs and swap sim cards *will i need my iphone the day of the launch? cuz then i will cancel my existing data plan on my iphone 3g even though i would have already sold it to my friend cuz the money hes giving me for it is whats paying for my 3gs* will this work flawlessly? if she activates an unlimited data plan for (her) iphone 3gs will i be able to use that still after i stick my sim card in the phone? does that plan apply to the sim card or the device?