I still have no LTE no matter what I do.
i have a 950XL dual sim, unlocked, bought from US online microsoft store.
I had my previous sim card from a Lumia 520 (my previous daily while i waited for these) and i chatted with ATT online and had them provision it for the an ATT 640 that i had that was unlocked.
I checked that the 640 had LTE.
Then chatted with ATT to try and get the imei of the 950XL provisioned... they tried but couldnt get it working... told me the "two weeks" story like others have heard...
Only had Edge sometimes, not even 4g.
SO i gave them the imei of the 640 again and popped the sim card back into the 950XL.
Then i did a hard reset - from the update menu...
but when the phone restarted i did NOT allow wifi to be setup - told it to continue with apps etc. first.
Then went to APN settings, created new APN settings for ATT but did NOT apply them.
Turned off cell data.
Applied the new APN settings.
Turned on cell data.
Had Edge data when i needed it now, instead of not even getting anything.
Then about 30 minutes later, LTE popped up.... and about 6 days now of LTE without it losing it... in various locations... speed tests show about 7Mbs up / 9 down at work and about 27Mbs down and 9 Mbs up at home.
Not sure what exactly did the trick, but i think it may be the hard reset and not allowing wifi to be setup during that initial setup screen.
Also, during the last chat with ATT rep - who seemed more knowledgeable and had a 640 himself - he told me to go outside and get clear of buildings to get the tower to see my phone... not sure if that helped, but that is worth trying also... as you know some Bands have trouble penetrating buildings...
Good luck...