Just picked up a Gold 5s T-Mobile iPhone. I racked my head over all the answers given here on the forums. I have ATT and jumped on this device so as not to wait another 3 weeks. I opened the box which is not labeled with anything other than model number that I could see...and popped out the pre-installed T-Mobile Sim, popped in my ATT Sim and bam LTE popped right up on the ATT network. So from the APPLE STORE the phone is unlocked. NOW....there is one caveat....
If you are coming from a 4G/3G phone...LTE will not pop up on the phone...why? Well the T-Mobile 5S IMEI's actually pop up in ATT's system as a 4S. Its a known issue that ATT is working on. This happened to me because I actually was upgrading my wife's phone which was 4G. So ATT worked with me by using my android IMEI to provision the Sim and then got LTE working on the 5S....and all is now clear...luckily I got a good rep at ATT...if your coming from an LTE phone then no worries it will work without getting ATT involved.
Hope this helps clarify a lot of the confusion out there, I just finished getting this all setup.
One other point....I assume the Apple.com version of T-Mobile works the same but I cannot confirm.
If you are coming from a 4G/3G phone...LTE will not pop up on the phone...why? Well the T-Mobile 5S IMEI's actually pop up in ATT's system as a 4S. Its a known issue that ATT is working on. This happened to me because I actually was upgrading my wife's phone which was 4G. So ATT worked with me by using my android IMEI to provision the Sim and then got LTE working on the 5S....and all is now clear...luckily I got a good rep at ATT...if your coming from an LTE phone then no worries it will work without getting ATT involved.
Hope this helps clarify a lot of the confusion out there, I just finished getting this all setup.
One other point....I assume the Apple.com version of T-Mobile works the same but I cannot confirm.