ok, I have some data .. I'm seeing similar issues that estnet reported here in Bangkok at the SGS, inability to hold and lock onto a signal. They seem to be using TRUE here. Though I noticed my wife's nexus 5x had a signal at times when my iPhone did not.

It is t-mobiles call as to who the choose to partner with. I don't know why people are referring back to t&cs and crap like that. It either works reliably it doesn't which is kind of the point.

My local SIM is TRUE-H and it does not get a great signal either at the SGS, but fortunately the hotel has great wifi and you can just turn on wifi calling.

I hope it works better in Europe.

-David