I’m going to add my two cents here. Through a quick scroll I didn’t find it, but maybe it was mentioned before, in which case I apologise.
I am presently in the USA. At home, I use an Italian Iliad sim card without any problems.
I bought a prepaid Ultramobile sim card here, which works well for my needs (data and texts; haven’t called yet, but it even registered on VoLTE once, I think).
BUT, if I put them in together, the Iliad card gets “deregistered”, and doesn’t connect anymore, while the Ultra keeps working as before.
The only idea I came up with is that maybe there’s some sort of conflict. Iliad uses AT&T’s network, while Ultra (Walmart’s MVNO) uses T-Mobile. When I try to select SIM1 (Iliad’s) network manually, only T-Mobile shows up.
If I insert only Iliad’s card, AT&T networks show up.
So, maybe two different carriers cannot work in the same phone?
