I have an old Sony Ericsson dumbphone and an iPhone 4S. What I ultimately want to do is sell my 4S and use the dumbphone (without making any changes on my account) until the next iPhone comes out. I thought I would be able to use my microsim in the dumbphone using an adapter but it won't let me. I did some research and found out that iPhone microsims are specifically designed for the iPhone and won't work with old dumbphones. Well what do they make microsim adapters for then? Today I was told by an AT&T rep that if wanted to activate a standard sim to use on the dumbphone, they would have to adjust my plan accordingly, meaning I would lose my grandfathered unlimited data plan. I'm pretty sure I'm not the only person who has tried to do this. What would be the best route to take?