Sony Ericsson P900

If you already have GSM service, all you have to do is insert your SIM card. If not, all you have to do is go to the carrier of your choice and purchase a SIM card and activate it at that carrier. I was using T-Mobile service, but I just got too many dropped calls when I'd travel throughout the US even though their plans do have more minutes for less money. I currently have ATT Wireless and I get better reception tan I ever did with TMobile. I get calls in places where I never got service with TMobile. My suggestion to you for carriers is check with other people who have different carriers in your area where you live and their experince with reception, dropped calls, etc. and also in areas where you may travel for business, personal, or vacation, especially if you travel a lot. For example, I live in a large city and I could travel a mile down the street to a friends house when I had TMobile service and my phone would get no reception until I left that area.

Do your homework on the GSM carriers in your area.