If the phone is lcoked to Sprint then you need one of their cards to unlock it Borrow a card from someone. It doesnt need to be an active sim. If it is not locked use any sim to activate the phone. To use as ipod read
USING AN IPHONE AS AN IPOD
Restore your phone as new. Place a SIM card into the phone and connect it your computer with iTunes open and follow the activation assistant to activate the iphone. Once the iphone have been activated remove the SIM card and turn on imessage in settings/messages. Only your Apple ID should appear in the “You can be reached by imessage at” and “Start new conversation from” fields. Read the following article for help http://support.apple.com/kb/HT3406