Help if you can

So, this may be out of some people's range on here, but, I recently got back from germany with my partner, and he had to buy a new iPhone while he was there. Now, it turns out that it was the international iPhone 5 (A1429), and he figured that "Eh, it won't support LTE..". And yesterday when he put his T-Mobile SIM inside his phone, the Data Slider said LTE on it, and not 3G or whatever it might say, and that baffled us. So I was wondering if anyone could clear up anything that might help us understand our confusion?

 

I think since T-Mobile uses GSM signals which is the same as international phones you should be good in the US. LTE is part of the GSM standard.

This article probably does better at explaining it than I can: http://geekbeat.tv/a-guide-to-cellular-radios/

Thanks