New line on amazonwireless

[altimax98]

With all these big deals online with the holidays Im figuring that the Gnex may go cheap on amazonwireless. Ive got two lines now, and my mother in law needs a new plan. So I was going to give her a dumbphone (craigslist) and buy a Gnex on the new line but activate it on my line and activate a dumbphone on hers (so i can get the new line disc). I know through verizon you can do this but what about amazon?

Thanks in advance!