Dual SIM iPhone Support
Ok, so with the addition of dual sim support in iOS 12.1.2 I went and got an iPhone XS Max so I could consolidate my iPhone X (personal) and iPhone 8 (work) into a single phone.
My Cellular Accounts
When I initially called T-Mobile to setup my primary number as the eSIM, I was told it is "not possible to do with post paid accounts at this time". Fast forward, that was bullshit and it’s totally possible. Once I got that going, I then popped in my work AT&T physical SIM card as the secondary line. This was now working, but there was one major caveat. Only one line on a phone can be associated with iMessage and FaceTime. This was unfortunately a deal breaker since I needed iMessage for both of my numbers.
It was definitely weird to see two sets of signal bars in the iOS status bar! It was also interesting to see how the system handled the distinction of your primary and secondary number when it came to calls, messages, etc. The system added a distinct "P" or "S" logo prepended to entries to identify which line they belonged to. This also carried over to my Apple Watch.
Unfortunately because of the inability to use iMessage with both numbers, I had to go back to two separate phones. For now..
I am going to revisit this in September with the next batch of iPhones and iOS 13.