international sim card ?

heather, Even though you have an "unlocked phone", you'll need to verify that it's a quad-band GSM model, and equipped with the two European frequency bands. It would also be a good idea to check the Charger to ensure that it's designed for "world operation". You will of course require two different types of Plug Adapters (Europe and the U.K. use different styles). Due to the fact you'll be in a number of different countries, I'd suggest having a close look at the "travel phone" firms, such as Call In Europe, Roam Simple, Telestial, Cellular Abroad or Mobal. You can obtain a SIM from them, usually on a post-paid basis, with calls charged to a credit card. The rates will be consistent regardless of which country you're in. That will also provide you with a working phone as soon as you arrive in Europe. If you purchase a SIM in Rome, it will provide the lowest rates when used within Italy but calls will be more expensive in other countries as you'll then be "roaming". Therefore you'll have to "top up" more frequently. Happy travels!

Thanks for the info! It's an iphone first generation and an iphone third generation.

heather, I'm not entirely clear on your last reply. Are you using a first generation or third generation iPhone? Do you have two unlocked iPhones? The fact that you're going to be travelling with an iPhone of any type raises some significant "red flags". Are you planning to use to phone only for voice and text, or also for data access (ie: web surfing, checking your E-mail, etc.)??? BE SURE to switch off the data roaming prior to arrival in Europe and use Wi-Fi as much as possible! If you were to travel with a SIM from Mobal, Roam Simple, Call In Europe or one of the other travel phone firms, this would most likely ONLY provide voice and text, and NOT data. You might also have a look at the plans offered by iPhone Trip, although the cost would be about $15 a day. If you currently have a cellular data plan with AT&T, you might check their roaming packages as that might be a cost effective option if you're just planning to use the phone occasionally.

I highly recommend the Mobal Card, I have had mine for years. I only use it for emergencies since the rate can be high depending on the country. It is good for 180 countries, not just Europe. You can give family & friends your # since it is yours forever.
If I am going to be in one coutry for an extended time I purchase a local SIM, then I notify family/friends of chg in # usually using email or skpye to do that.