Yeah, I PM system may work nicely, but then can also be an annoyance if you don't want to get messages from certain people. May also be complicated for the dev team to implement properly.
I don't think I'd want to message each person individually, that is not ideal. :)

I work pretty much normal work hours, but on standby at night's every second week. Sometimes I'm required to be available when work is done after midnight in production environment, which they can't work on during normal hours. Planned work like this is fine, but when the guys mail me late afternoon to be available for 3 or 4 hours at midnight, it is quite annoying, especially if I had worked the previous night. I'm allowed to claim compensation for it, but if I decide to take the morning off (half day), then no monetary compensation.

Out of curiosity, what do you work on/as if you're working at night?