You need a nano sim. Is the phone unlocked?

On the back of the phone there should be a model number starting with the letter A. Type that model number into google and find out of the phone is locked to a carrier or unlocked. If it's a locked phone, you'll need to obtain a SIM card that matches the carrier. Sometimes the carrier retail stores or the Apple store will give you a SIM card for free... sometimes they'll charge about $10. The SIM card doesn't even need to be active... it just needs to be present to "activate" the phone.  If it's unlocked you won't need a SIM to activate it.

Make sure you check if the iPhone has "Find my iPhone" enabled. I've encountered many used iPhones with the lock and it's nearly impossible to bypass without knowing the previous owner's Apple ID password.

http://www.amazon.com/Sprint-Nano-Card-iPhone-SIMGLW406R/dp/B00IVUWO8M?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00

I bought this one for my sprint iPhone 5. Works on FreedomPop.

poor spurgeonryan junior... now he'll go from free wifi to free wifi spots for the rest of his life...