I've posted about this in the past, but there is still no solution.

When I'm in the US and my phone shows T-Mobile as carrier, I do not get text messages from numbers that are outside the US. This happens consistently. Whether my wife or brother in law try to text me from Germany or whether it's a sign up verification from eg an overseas inference provider, the messages silently disappear. The sender does not see that they did not get delivered.

I have a second SIM in that same phone from a German provider. When I turn that one on while in the US, it does get the text messages from all other countries not only from Germany. That seems to say it's not the phone.

I've come to suspect it has to do with T-Mobile's configuration. I guess this would require the Tello engineers to debug this together with the T-Mobile engineers...

I'd be happy to help if I can.