I just got a OnePlus 6T and switched to Mint Mobile. Sending and receiving SMS works well as do phone calls. I started a group message (MMS) with two people and when I send a message it sends and they receive it. However, I can't receive any of their replies. They are on iPhones, which is what I switched from. I have searched the internet and the forum and found similar issues, but most say they were fixed by manually setting the APN to Ultra/Wholesale.