This thread is very interesting and I guess thanks for posting it up.

I've been wondering if I should switch to T-Mobile to save on the roaming data, but it seems it's not working that well everywhere. I know for LTE roaming your home carrier needs to sign new agreements with the roaming carrier, so I assume T-Mobile USA hasn't done this? This would explain why it works on T-Mobile DE only since it's technically the parent company there is no agreements needed.

I ask this because I currently have AT&T and when I roam it connects to any available network (including LTE) on just about every place I've been to. It even works on cruise ships and you know how restrictive [and expensive] those are. The only issue I have to roaming voice is very expensive, so I forward all my calls to my Skype account which I can answer with via data.

So I've been debating switching over for a while now. I'm current paying $65/month for the data plan, but my roaming voice is like $2/minute.