What a bunch of jokers...
Edit: I think it says a lot for Ledger's performance that it wasn't until after the movie that it suddenly struck me, "That was Heath Ledger, the blond Australian dude in 10 Things and A Knight's Tale." I was never once reminded of the man under the makeup during the entire course of the film. Also this...
Definitely a nice touch. Totally threw me for a loop.
Fair enough. Joker's is the only that's explicitly shown, but I do think it's implied that the henchmen, hostages, and SWAT teams had some form of cellular communication.