Good reasons for why T-Mobile only wants VoLTE phones now.

[Shilohcane]

With VoLTE then T-Mobile's customer can have both data and voice calls roaming on another network over their LTE. This VoLTE gives T-Mobile a lot of new options to improve nation wide coverage even in rural ares with new partnerships that weren't compatible before VoLTE to expand their network coveage. Here are two new deals that VoLTE has opened up for T-Mobile to expand it's network for their customers that have phones that support VoLTE.

T-Mobile joins CCA's LTE data roaming hub to expand reciprocal roaming deals with smaller carriers

also,

T-Mobile affiliate iWireless aims to launch LTE in Q3, strikes LTE roaming deal with T-Mobile

 

[Rukbat]

Not quite exactly accurate. 2G is universal in North America. A roaming contract with any carrier made any TMobile phone frequency compatible with any roaming partner's towers. Now they need a hub to be able to handle any of the LTE frequencies in use. It'll make the switching and billing (if you have a limited plan) easier, but it takes a lot more tower technology.

(Eventually, someone will notice the word "standard" in the dictionary, and we'll have some. That will make it even easier.)

 

[Shilohcane]

Not quite exactly accurate. 2G is universal in North America. A roaming contract with any carrier made any TMobile phone frequency compatible with any roaming partner's towers. Now they need a hub to be able to handle any of the LTE frequencies in use. It'll make the switching and billing (if you have a limited plan) easier, but it takes a lot more tower technology.

(Eventually, someone will notice the word "standard" in the dictionary, and we'll have some. That will make it even easier.)

1G was the original universal standard but it was replaced by 2G. Verizon has even said they were moving away from 2G in the near future but plans always change. Fact LTE gives T-Mobile more roaming partners as long as the networks and phones support VoLTE.

T-Mobile is moving towards a 100% LTE Network. Granted it will take a few years.

 

[Shilohcane]

T-Mobile responds (off the record) to why they now require Band 12 phones to support VoLTE since they are require to by law to support E911 on Band 12.

" The problem is that E911 compliance is inextricably linked to T-Mobile's VoLTE requirement for band 12. Without VoLTE support, a device on band 12 service would be unable to make phone calls of any kind if no other T-Mobile band was available (it will not know to fall back to AT&T roaming - the call will just flat-out fail), and that would include making 911 calls, meaning the device would for legal purposes likely be out of E911 compliance, and T-Mobile could get in trouble with the FCC. "

 

[Citizen Coyote]

If T-Mobile really wants to improve their network, it seems they would work to minimize the hassle for OEMs to get their handsets certified to use VoLTE on T-Mo's network. As it stands, T-Mo is the only major US carrier that uses Band 12. I assume they want manufacturers to include Band 12 support in new devices, yet they require them to jump through hoops to get VoLTE to work. I understand they need something to ensure the phones work properly, but given that several OEMs have simply disabled Band 12 support rather than go through the certification process tells me T-Mo needs to streamline it. They made a name for themselves by being friendly to BYOD users in the past, but the current Band 12 brouhaha is a strike against that.