Putting service on an iphone 4?

So about a year ago in my place of work, someone had found an iphone 4 and put it in the lost and found. Our policy is that someone can claim it if no one comes back for it after 2 weeks. I immediately claimed it, however, waited about a month before taking it home with me. I have been using it pretty much for Wi-Fi and apps for like a year now, and have gotten really attached to it. I'm under a plan with verizon and want to put service on it. My sister is telling me now that the data plan is free for iphone 4s as long as you have a certain number of free gigs. Is this true? So could i just take this iphone to the apple store and have them put service on it and i wouldnt have to pay for the data plan? Would there be any problems with it not actually being my phone and someone elses?

That is not your phone, return it to the carrier store or the police. Chances are it was reported lost/stolen and will not activate.

I've never heard of Verizon having a free data plan for any phones.