I was trying to confirm tonight what someone had mentioned, about being able to call/text on a disconnected iPhone ~ and yes you can!
I upgraded to the iPhone 4s when it came out, and I have my old 3GS iPhone sitting here with me (with no service) that I charged up, connected to wi-fi and added a free app that gives you free texting and free starter minutes for calls (then you can buy 200 minutes for $4).
This is interesting - this phone doesn't have service, but I sent some texts and made a call. Maybe this is common knowledge to people who have their cells shut off. Learn something new every day.
So I guess we can conclude, that yes disconnected iPhones still have the
ability to make calls.