Screenshot courtesy of Infinite Labs
Infinite Labs’ free iPhone app…
Mover 1.0.2 (iTunes App Store)
…lets you copy contacts and images from one iPhone to another nearby iPhone over an WiFi connection. Based in the app’s description, both iPhones need to access to conventional WiFi LAN, however. This is not an ad-hoc network app. And, both iPhones need to have Mover installed (makes sense).
If someone in the group is carrying a MiFi 3G WiFi router, this app could be used pretty much anywhere without searching for a nearby common WiFi LAN to use.