You didn’t mention what device you are using. If it’s a Samsung I don’t know much there.
I have several devices on T-Mobile, all pretty much using the same APN settings.
I notice you have a “MMS Protocol” line with WAP 2.0. Over the years none of my devices have that so not sure what that’s about. A Sammy thing?
There are times when a default APN can’t be edited but usually one can add a new one.
The APN I use is mostly like below.
Name: T-Mobile US LTE
APN: fast.tmobile.com (the “-” was removed since the KitKat days, worked/works better with IPv4).
Proxy:
Port:
Username:
Password:
Server:
MMSC: http://mms.msg.eng.t-mobile.com/mms/wapenc
MMS proxy:
MMS port:
MCC: 310
MNC: 260
Authentication Type:
APN Type: default,supl,mms (sometimes with ia).
APN Protocol: IPv4
APN roaming protocol: IPv4
Turn APN on/off: Grayed out unless there are multiple APNs
Bearer: Unspecified
With some ROMs/devices you may find a separate APN for MMS (as on my Axon 7). As such the MMSC will be blank in the main data APN.
Name: T-Mobile MMS
APN: TMUS
Proxy:
Port:
Username:
Password:
Server:
MMSC: http://mms.msg.eng.t-mobile.com/mms/wapenc
MMS proxy:
MMS port:
MCC: 310
MNC: 260
Authentication Type:
APN Type: mms
APN Protocol: IPv4
APN roaming protocol: IPv4
Turn APN on/off: Grayed out unless there are multiple APNs
Bearer: Unspecified
On occassion I have issues with sending/receiving images but that’s related to VPNs and the like. Have to apply workarounds until it happens again.
On a side note, all of the devices except the new one (with 5G) have a T-Mobile IMS APN. IP Multimedia Subsystem, in theory that means support for VoLTE should be present. Maybe, as per this article last year, along with a way to test…
T-Mobile and AT&T will require VoLTE for calls after shutting down 3G
EDIT: Re-read your message again and missed the MNC 240 thing. 240 (freq GSM 1900) is apparently invalid/old/not_operational according to various sources. Can you create a new APN with 260 and see if it sticks?
Here’s a related thread from reddit.
MNC Stuck at 240 not 260: USMobile