Switching to T-Mobile

I haven’t been keeping up with all the T-Mobile offerings so I have no idea what are some of the better deals out there to switch to T-Mobile.

I have a friend who is on AT&T and planning to switch to T-Mobile. He wants to move 6 current lines and add 5 new lines. Interested in getting new phones as well not on all the lines but on a couple.

I told him about the insider code but what would be his best option in this scenario? Appreciate everyone sharing their knowledge and time.