I don't even have a data plan for my iPhone 4s. All the usual cycling/activity apps work fine. Just needs GPS sync. I mostly use Cyclemeter (paid version, only $10) and Strava (free version), but have tried Ride With GPS, Map My Ride and others.

They all work pretty much the same for recording rides. Handy for revisiting a good route or avoiding one that wasn't so good. But Map My Ride is probably better suited to exploring rides other folks have ridden and commented on.

WiFi at home handles data uploads, etc. Occasionally I'll carry a USB battery and cord to charge along the way on longer rides.