It is possible to hijack sessions only when WiFi is not using EAP, but it should work over any private networks (Open/WEP/WPA-PSK/WPA2-PSK) It's kind of like Firesheep for android.Maybe a bit easier to use (and it works on WPA2!).
FaceNiff is an Android app that allows you to sniff and intercept web session profiles over the WiFi that your mobile is connected to.
