Follow these directions to enable wifi calling:
APN: fast.t-mobile.com
TTL: 65
HL: 65
MTU: leave blank (Optional)
That’s it. BUT, all this really depends on the SIM card you have. I have a regular phone sim. I can send and receive SMS messages. I do not have a Home Internet SIM although I have set two of them up using these same settings. When using the Home Internet SIM, it is critical to clone the IMEI# of the TMHI router. Directions for that can be found somewhere else on this forum but since you said you do not have TMHI, I’m not including a link here.
My phone only gets one bar(many times SOS) and about 5Mbps where I’m located but my GL-X3000 gets 3 bars(5G SA) and between 80Mbps and 140Mbps depending on the time of the day. I couldn’t be happier with the connection since I’m close to a military airport and there are NO cell towers anywhere near me. The WiFi calling has been a life saver with this router