Yes. Even 3g to LTE are different. I know you can still get a data capable sim to work in a dumb phone because I've had to do it, but I don't think opposite will work. Also, different size sim cards. Full size, micro and nano. My 920 takes micro. Don't know what 620 takes but I would assume micro as well. Never seen a feature phone that didn't have a full size sim. I have seen people cut down some Sims to fit. I could be wrong with feature sim working in smart phone. That would be something to ask an att rep and they will probably tell you no regardless of if it will work.