Using Verizon's S6 on Tmobile's network

[Sotat]

Hi all, has anyone here tried or been successful in getting the data or lte over voice calls with Verizon's S6 using Tmobile? I have Tmobile and trying to use my gf's unlocked Verizon Galaxy S6. Almost everything works fine except that while on voice call, the signal drops to 1x and I can not simultaneously use data or receive mms. Are there any fixes for this? Any help would be appreciated as she is planning to switch from Verizon to Tmobile and I would love to just reuse the phone on Tmobile.

 

[AlphaTango414]

Turn on VoLTE. Setting>connection>Mobile networks>mobile data