I am thinking of buying an unlocked GSM phone. I've been looking at Sony Ericsson and a few others, but I have some technical questions on what all it means to have an unlocked GSM phone. I understand the basic concept, but I keep seeing some inconsistencies with the details. For one: I see carrier compatibility issues with different phones. I've found a whole list of carriers with GSM compatibility in the US (AT&T, T-Mobile, Cincinnati Bell Wireless, ECT...). Now, does that mean that if I own, let?s say the Xperia x10a, I can use any GSM carrier? Will that vary from phone to phone? Will any GSM carrier accept any unlocked GSM phone? Also, if I own an Unlocked GSM phone with 3g and Wi-Fi capability, and dont want to pay for the mandatory data plan because I can do just fine with Wi-Fi for my needs, can I do that? Will that depend on the carrier? That's the big one for me. Any help on these questions would be greatly appreciated. Thank you in advance.