Hi all - this site has helped me so much that I have to share what I just found out. I have seen plenty of times on this site that people will purchase an inexpensive unlocked cell phone from eBay or Amazon or wherever to take with them to Europe so they can buy a European SIM card. Well I read somewhere online that if you have had your phone for longer than 3 months, it's possible to call your carrier and tell them that you are travelling overseas and ask if they can unlock your phone. I have ATT and I just called them and sure enough: they are going to give me a code to unlock my phone for free! All you need is your IMEI (which I couldn't provide because I was talking on the phone I need to unlock) and be caught up with your payments. Of course, your phone must be quadband to even function with a European SIM card, and I am not sure if all phones will qualify for this or if all carriers are as copperative, but it's worth a try and it might save you a few bucks. Plus, you will have the convenience of having your own phone (contacts, pictures, etc...) while travelling. If this isn't new info - shame on your for not telling me! :-)
But if you find this helpful, please let me know if it works for you when you try it.
The carriers can give you an unlock code for most types of phones, but not all. Unlocking the phone may require that you put in a SIM from some other carrier, but not always. E.g., a T-Mobile SIM in an AT&T phone. Sometimes you can get to the unlock sequence from a menu. The unlock code should include instructions for how to do it. Ninety-five percent of the time these instructions are correct, but there are occasions when they are not. I have had to search the Internet to find out the proper way to unlock some of the phones I have. It usually helps to tell your phone company that you need the unlock code because you're going out of the country. They all understand what that means.