I like to buy my own phones and bring them to my plan. Sometimes this results in not having the full config to make the phone work 100% on a carrier. I recently fixed issues where I could not receive MMS messages if I had an active wifi connection. When my phone is on wifi, it chooses to send and receive messages and calls over wifi instead of the cellular service. Unfortunately, I was missing this in my APN config!
APN settings: (Changes I made to my settings in brackets. Full quote is from source)
Name: T-Mobile US LTE
APN: fast.t-mobile.com
Proxy: Not set
Port: Not set
Username: Not set
Password: Not set
Server: Not set
MMSC: http://mms.msg.eng.t-mobile.com/mms/wapenc [ADDED THIS]
Multimedia message proxy: Not set
Multimedia message port: 80 [ADDED THIS]
MCC: 310
MNC: 260
Authentication type: None
APN type: default,mms,supl [ADDED mms to my existing list]
APN protocol: IPv6
APN roaming protocol: IPv4
Enable/disable APN: APN enabled
Bearer: Unspecified
Mobile virtual network operator type: None
Mobile virtual network operator value: Not set
Source: https://support.t-mobile.com/message/626402#626402