can my mother use her upgrade to get me the iphone 3g at the discounted price?

My iphone was stolen a couple days ago, i had it for 1 day! Some loser stole it from my dorm. So i've already used up my upgrade, and in order to get a new one i'd have to pay twice as much or more than what i originally have. Now, since my mom hasn't used her upgrade she can do this, anybody know if there would be a problem with her handing the phone to me and activiting it under my line (we have a family plan) a couple days later?