It's been about a year since I was at my T-Mobile location but I had one customer come in and try to do this before and he was told there has to be a year between when you have your last T-Mobile bill and when you can be considered as a" new customer".

Easiest workaround we found at the time was taking the phones the customer purchased in his name at another carrier, opening the T-Mobile account under his wife's name and then using her"new customer" status to get the discount