I JB'd an old 3G, and I was wondering if I could switch sims from my iPhone 4 to the 3G whenever I wanted (made an adapter) to mess around with the JB for a day without having to make any account changes on my bill or anything (AT&T). Sorry if there is a thread about this already. I MRoogle'd but found only things about sim swapping from 3Gs to 3GS's. Just wanted to clarify about the iP4 to 3G.