What do I do with my iPhone 5c?

Okay so I bought a used iPhone 5c off of Craigslist and the guy took out the SIM Card.
It says I can't use the phone until I get a SIM card.
I don't even have Sprint! I bought the phone with the intentions of using it as an iPod and the guy told me it was possible.
So I went to Sprint and asked for a SIM, the guy asked for my phone number and I told him my phone didn't have line and that I only wanted to use it as an iPod.
He said he couldn't provide a SIM card unless I had a line with them (greedy people am I right?).
So now I have an iPhone 5c I bought for $200 that I can't use.

Why not just go to CVS and buy a $20 phone to take the SIM out?