Just because T-Mobile operates service in other countries doesn't mean anything. Naturally, it's very likely that your US T-Mobile SIM card will roam on T-Mobile abroad, but so will Cingular (depending on the area). I've been to the UK and NL (empeg meets) with Cingular and the reception is as good or better than at home.

You and I live in roughly the same area. I used to have T-Mobile. Cingular beats T-Mobile hands-down in the metro NY area. A lot of rural GSM providers seem to use 850MHz which T-Mobile doesn't go out of their way to support. Since this is one of the bands Cingular operates on (as well as 1900MHz in the US), rural providers really fill-in the gaps nicely. I'm roaming on CellularOne right now at home. Something I couldn't do with T-Mobile because their phones generally omit 850MHz and they seem to have no roaming agreements with 850MHz providers.

As far as Cingular knows, I have a Sony Ericsson T637. Being a "standard" mobile phone, they give me unmetered data for $19.99 per month. Tethering my laptop to that phone was never a problem. Since that phone, I have moved-on to the Motorola A780 and now have the Qtek 8310. Both of those are PDA-type phones. I still have the $19.99 unmetered data plan. At the time I moved to Cingular, their unlimited data plan for PDA phones was like $80!

Cingular is also rolling-out their HSDPA data service now with an all you can eat plan for $20 (so I heard). HSDPA is based on UMTS and is backward compatible. So, your phone will work on UMTS, Edge, and GPRS data networks abroad.

My commitment to Cingular is up and I'm still with them. That should say something. I've gone from Bell Atlantic Analog to Verizon CDMA to T-Mobile to Nextel to T-Mobile to Cingular and I'm happy where I am right now.

Verizon is out of the question. No GSM = your phone number doesn't leave North America. Get even as far as Aruba, and you're SOL.