The moment you really become an office employee is when your phone rings when you're discussing something with a co-worker and you have to excuse yourself in order to pick up (you realize at the same time that you're still an intern because you have to pick it up if you don't want whoever's calling directed to Some Guy's voicemail, but that's beside the point). Better yet, it's actually another co-worker calling to ask you something.

(because yes, as an intern, most phone calls you get here are personal. so it's a nice change.)