Last year, I took out the sim that came with the phone and put on mine and turned it on and it ruined the phone. I don’t know why. I have never seen that happen before, but it cause a lot of headache. I know if I activate this years phone under my mother in law’s upgrade, it will transfer her number to the sim that came in the phone. This has happened to us before. They don’t live too far away, so I’m just going to drive the new sim over to her and be done with it. Obviously you can’t do that.
You can try to just put your sim in before you turn on the phone and see if that works. Like I said, that didn’t work for me last year. The phone wouldn’t activate. Maybe it was just THAT phone. If you do have to activate your brothers number on the new sim, a call to customer service with his old SIM card and imei number will fix it. It will be a pain, but it can be fixed.