To Hijack a Facebook or other service session you need a Rooted Android Phone, More Info (xdadevelopers) google it.
Then this little apk called faceniff http://faceniff.ponury.net/.
Basically this will be installed on your phone putting it wireless card in promiscous mode and stealing all the sessions allowing access to the account. This only works on wireless. If the users is using SSL (HTTPS). Never use an open WIFI.