I was planning to do this as well. I hope somebody else out there has tried it already.
My spouse is headed to Europe in April and the whole family is going in June. I supposed he can be our guinea pig if we don't get any replies to this post. I'll keep you updated after he gets back late in April.
Yes, just came back from Europe and everything worked, texts and data at no extra charge. I have simple choice and the international plan added to it. That plan is usually $10/mo, but I read about a discount somewhere and asked customer service about it in December, so now I only pay $5 for the international plan on top of the simple choice plan.
I just happened to have the intl plan, because I use it to make international calls, but I think you don't need it for the free data and texts overseas.
Just make sure your phone is unlocked, if it is not a T-mo phone. If you are not sure, buy one of those 1 cent sim cards with free shipping from amazon that is different from your own carrier to test it.
I don't remember, sorry, but I do believe it is very much throttled by T-mo. I could get emails and such, but would not have attempted youtube, for instance.What type of data speeds did you get in Europe. I have heard from other T-Mobile that the data speeds in Europe are 2G for the free roaming. I would love to get a T-Mobile sim if the speeds are decent. Right now I just get a prepaid European sim when I arrive in Europe.