Are you asking if each member of the family can get a separate equipment installment purchase plan(EIP), or if you can switch more than one phone over? As far as the EIP, no it all goes on the same bill but is itemized and you can finance all the phones if your credit is decent. As for switching a family account, yes I believe they allow up to 5 lines and each line switched gets the promotional credit as long as you hand in a phone per line. You can find out what the credit will be by asking tmobile. They had a special for Sprint recently but i don't know if it is still available. Regardless they still give prepaid visa mailed to cover early termination fees from your old carrier. The number switch takes a few hours. Pretty painless.
I switched from VZW last year and moved all 4 of my lines over and got a tablet line for my fifth. After a year they let me add more lines. Yes, I give Tmobile a lot of money every month lol.
Tmobile is also very good about responding to twitter so you can always send them a message if you have questions. Or better yet bring your bill into a store and get hooked up!
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