You’ve already checked off the two most challenging parts of adding a new line to your account: Identifying who you want to share. Webadding a line for free phone promo, then cancelling an old line. I am currently on magenta for 2 people. I want to know if the following is possible: I add a 3rd. Webi want to add them on my plan for unlimited date but they also want to upgrade and keep their number. How should i add them? He needs to port over to your account and you will be the new line owner if you're the pah. Webbeware all customers trying to add a current promotional line to their grandfathered simple choice plan! Tmobile said my line qualified and it would be. Webi currently have a plan of 4 lines on magentamax, with insider discount and a free line in place. But, i am thinking to port another line to this current plan. What about be the most. Webgenerally there is a time limit. It should be in the terms. From some of the other promotions some you couldn’t have gotten rid of any lines 3 month prior to the. Webno you cannot but there is nothing stopping you from canceling a line after you get your device and new line added. The terms say you cannot cancel a line 90 days before you.