Hi Everybody,this is my first post, if it's been mentioned somewhere else on this forum, than I apologize about it.I got my nice shiny Nexus 5X last week and I have immediately realized, it does not connect to B12 on T-Mobile. I saved some network logs on My old Motorola Nexus 6 and on my new 5X and it was clearly blocked. This phone should work on B12 right out of the box, therefore the immediate OTA update was suspicious for me. I was right, it was not only a monthly security patch, they have also "downgraded" the base band for us, just because a FCC approval is missing (911 access on T-Mobile's VoLTE), however on Project Fi we have E911... We still should have a Project Fi specific firmware until FCC approves T-Mobile's application...I have downloaded the very first official ROM (MDA89E) and extracted the radio and flashed with ADB on my device. It is working flawlessly with the latest "I" firmware and MOST IMPORTANTLY I DO HAVE B12 on my phone.If you'd like to try it, please do it. Remember, I'm not responsible for any damages, flash it if you exactly know what you are doing...The radio(baseband) version what I flashed on the latest MDB08I is: M8994F-2.6.22.0.56If it's worked for you, than do not hesitate to hit the "Thanks" buttonUpdate on 12/07/2015:The New MMB29K 6.0.1 update has a new radio, which is finally T-Mobile B12 compatible. (radio-bullhead-m8994f-2.6.30.0.68) Looks like Google and T-Mobile silently "solved" the issue. There is still no official announcement...