I didn't answer the cell phone vs. landline one, because it's dependent on the person. I have friends who turn their cells off or leave them outside the bedroom. I have called those people off hours to leave messages. In those cases, it's usually the fastest way to get in touch with them, since I know it won't disturb their sleep, but they'll get the message as soon as they wake up.

However, if I don't know for sure that their cell won't bother them, then I won't call it late at night.