After a couple of calls to PureTalk USA technical support (888-458-7740) I now have LTE working on a Lumia 635 using PureTalk's apn settings from the website--the ones labeled for LTE. On a Lumia you can tell if you are getting LTE as it says "Pure GSM LTE" under the bar graph giving signal strength. I ran a speedtest and got a bit over 25mbps download speeds and a bit under 4mbps upload. PureTalk runs on the AT&T network. Inexpensive prices for lower usage patterns, great US-based cs, fully autopay using credit card, no additional taxes or fees, free SIM cards. No hassles.