I don't have any 1st hand experience, although I would doubt that the 1800 carrier would be the best choice for widespread service.

For those of you who roam into GSM markets,
GSM overall is moving toward a more US-like roaming billing arrangement (surprise, surprise). Where in the past there was a fixed markup (15%, I believe) made by the home carrier to the records sent by the serving carrier, now they are starting to negotiate these rates (something the US carriers have done for years. This is a big change for many of the carriers.

Although technology-wise Europe is far beyond the United States, the USA has been actually more advanced on the billing and settlement front, with a great deal more flexibility for the carriers' operations.

As this is my business, I'll be glad to answer any questions here or to my email...

JL