Thanks for the clarification. So, the problem is basically this:
T-mobile has been shutting down its 3G network to make room for 5G, leaving 4G and any remaining 2G capacity to handle voice calls. Very soon its 3G will be all deactivated.
VoLTE uses 4G LTE to connect phone calls over the data connection, rather than over 3G (cellular connection). The benefit is ultra-clear voice calls.
A phone without VoLTE capability on T-mobile will require 3G or 2G to connect calls. As 3G is on the way out, that leaves 2G as the only remaining option on T-mobile. Even though a phone has 4G LTE, it also needs to be capable (by manufacturer/carrier certification) of using VoLTE for calls.
This is why T-mobile has also started requiring a VoLTE-capable phone for any new activation (as of last year).
Samsung uses a special proprietary software for VoLTE implementation, which at present can’t be duplicated by /e/ or LineageOS, the custom Android version that /e/ is based on. Therefore the phone does not have VoLTE capability; hopefully they can find a solution soon.
It sounds like you have encountered a location where T-mobile doesn’t have much remaining 3G coverage, if any. This will always result in calls not connecting, and probably not even going to voice mail or giving you any indication that there was an incoming call at all. You may have had some intermittent connectivity if there was some semblance of a 2G (or sporadic 3G) connection, which is probably why you eventually got the texts to send.
As workarounds, I can think of only three:
- Change network to AT&T (or a cheaper AT&T reseller). Their 3G network isn’t shutting down until next year, so that buys some time.
- Change phones. If you still want an /e/-based device, you’ll have to find a phone that is both equipped with VoLTE and on which /e/ is capable of being installed (excluding Samsungs, of course). You’ll have to most likely do it yourself, or get someone to do it.
Edit: I believe /e/ is selling Teracube phones for the U.S. now, and they do have VoLTE enabled. - Wait for /e/ to say if they can fix it (as long as you have mostly good 2G/3G coverage where you are most of the time, but keep in mind the network is evolving/devolving).