Making outgoing and receiving incoming calls
I have a SGS9+ (unlocked). Each time I swapped in a different SIM card from different company Carriers/Providers, their logo is what I see when I reboot my phone. Now It doesn't, happened right after I put in a SIm card from ATT. Now I inly see the ATT logo and apps that came along with the SIM. I also was able to make calls and receive calls for aboit a week until i couldn't, it allows texting and use of data but the calling feature. Tried to have support and have done various research on the fix but in the end, I got fed up of rrying to dig any further into it and settled with what I already have. GOOGLE VOICE! It's free works fine in both calling and texring to anyone, anywhere within the NA or Canada and a lil'bit of charge if I wanted to make out of country feature (don't need it). Only downside of this is it is VOIP so using a GV# on some things which requires an Offical phone# from providers isn't allowed. For that i use the ATT cp# to receive texting. Hahaha..
I have also inserted att sim card into my unlocked tmobile device and everything works in it. Until att detected thag the phone isn't from att so they blocked it for everything (calling,texting, data). Now the sim only works for my sgs9+ with ofc the blocked calling option by att..
Anyways.. I have att data and texting and I use GOOGLE VOICE for both calling/texting as long as i have internet connection (att data).