hi all i have an iphone 3g and i am thinking its time to upgrade to a 4. i was wondering could my wife pop her sim card into my 3g and use it without a rate increase (we are on same plan) oh and if it matters her phone is one of those shitty free ones ............. also since i am under contract (i am eligible for an upgrade though) do i even get to keep my 3g?.........also are iphone 4s sold out still or are they pretty easy to find