Got any sources to back this up? Because all of the gear carriers use is off the shell Ericsson/Siemens/Huawei stuff, and LTE mandates LDAP for subscriber information (most of them use OpenLDAP) - the only thing that really differs in their infrastructure is their billing software that manages subscriber data in the directory.
The only physical difference really is RF spectrum, and most phones released these days just cover every last LTE band their chipset possibly can (putting out tons of different versions is expensive, yo) - maybe limited to the specific bands used in the target region at worst.
In late 2014 bought an LG Optimus G E970 Unlocked 4G LTE phone, and it never connected with LTE on TMobile's network. So I had basically shit coverage except in major cities, but even in major cities it never used LTE.
Soon thereafter I got a Motola Moto G (XT1540) and even in podunk mountain towns I get LTE connections with the same Tmobile service.
>Soon thereafter I got a Motola Moto G (XT1540) and even in podunk mountain towns I get LTE connections with the same Tmobile service.
Band 12 (700mhz) made a HUGE difference in rural coverage in areas it covers.
Speaking of proprietary standards and stuf... Band 12 was held up in device support by AT&T (and some hw vendors) that claimed channel 51 television stations would interfere with their network without a new signaling standard and filtering. So they conveniently created a proprietary band 17 that cut off the lower-A block of spectrum that T-Mobile and other rural carriers owned. This had a filter in hardware so no devices supported Band 12 until early 2016.
AT&T of course, helpfully said they'd move to band 12 now that things are resolved. Didn't want to look anti-competitive or anything....
I also tried that. I got a phone off contract for really cheap (I think it was Verizon) and then tried to port it to T-Mobile. My connection was really flaky. I finally filed a claim on my insurance for my phone and switched to a nexus 5x. That solved the majority of my problems. Also each network is divided between bands, and phones sometimes only focus on specific bands. It doesn't really make a difference if your phone was made for a specific carrier, but if you are trying to transfer networks your radio might not be able to fully take advantage of the new network.
The only physical difference really is RF spectrum, and most phones released these days just cover every last LTE band their chipset possibly can (putting out tons of different versions is expensive, yo) - maybe limited to the specific bands used in the target region at worst.