Hold down home, if Siri pops up its a 4S(assuming Siri was enabled during initial device setup) if voice control pops up its a 4. But I can tell you right now beyond a shadow of a doubt that if it's jailbroken, it's a 4.
So my buddy redid his jailbreak and slowly started adding all his cydia stuff one by one. Were pretty sure he had to of DL a bad cydia package that was causing the safari apptstore and iTunes store crashes because so far after only downloading 3 packages everything is running smoothly.