It really depends on the country, your US service and your planned use Commander. I go to Europe a lot, London in particular so I have a system that I forward my US number to a US 800 number and forward that to a prepaid in England or a rental with free incoming calls in Japan for instance. If I had TMobile and just wanted it for someone to call for emergencies I would just turn on my phone and use it. Possibly Cingular too but their roaming seems more. If I were going to use it for a lot of calls I would use a prepaid in the country I was in. You can get them virtually anywhere in most countries. I think in Western Europe you are better of using your roaming than one of the international prepaids but check the exact rates in the countries you will be in. As I recall, where the multicountry ones really excelled is that some countries have really high roaming charges, say Tibet, while the international prepaids are mostly the same in all countries. I think in places like Italy, UK, France, Spain you are better roaming with TMobile at least.

So in my case, I have an unlocked TMobile SIM. I get to Heathrow and put in my prepaid SIM or just turn on the phone, depending on whether I have set my call forwarding. You do have to ask TMobile to activate international roaming on both voice, and if you want it data.