Can I switch lines in order to upgrade? VERIZON WIRELESS?

I have the LG Voyager from Verizon (without a data plan) and its ready for upgrade. My mom has the Droid for a year now but since she's not really using much of her data plan, is it possible for me to switch lines with her...so I can upgrade to an iphone using her data plan, and she's gonna use my usual plan than I have right now? Thanks in advance . (we're in a family plan btw --5 phone lines)