E-mail, voicemail etiquette

[markolas]

I tried googling this online, but didn't really find what I was looking for, so I thought I'd pose the question here.

What is an acceptable amount of time for returning e-mails or voicemails? Does it make a difference if their personal or business related? Should I be offended if I've left someone three voicemail messages in as many weeks and have still not gotten a call back? If someone goes months without responding to a personal e-mail, should I be annoyed?

And how do you call someone on this without sounding petty? I'll provide background to anyone who wants, but I thought I'd throw it out there as a general question first.