Do you think this will work?

I am in need of a new phone since mine keeps turning itself off even though I am not using any data plan and no applications are being run in the background. Since my upgrade doesn't come till November of 2013 I figure I would take somebody else's upgrade that is in my family. My mom said she will give me hers (her upgrade was in January of 2013). Unfortunately I would lose out on my unlimited data plan. I don't use that much but just starting out in the real world, I don't know if I may need that part of the plan. One of the cell phone (major) company representatives said that my mom could use her upgrade to upgrade her phone then the next day ask to go back to her old phone and i can then put my number on the new phone. Now that it is actually happening, my brother and mother are getting paranoid about it (well my brother is, which is influencing my mothers decision). Do you think this will work? or when we first explained to the representative who over heard my explanation said that it is "fraud"? he could of mis-interpreted what I said.