We have a universe of communication tools at our fingertips, but I see little consistency in how they are used.
How I like to operate:
Twitter: Great for general broadcasts, but you can't be hung up on who will and will not see it. Too much is outside your control.
I hate trying to have a private conversation via Twitter DM. Too little space, too easy to broadcast the private to the public.
Email: Much better for specific information and thoughts longer than 140 characters. Odds of your email message being seen? Pretty high, especially if the person you are emailing wants to hear from you.
Phone: Gotta know something right now, or i know a two minute call will replace a twenty email chain. Get the answer already.
Skype: Better than physically traveling, but often just a phone call with pictures.
Facebook: Not for work communication. Between you and customers, sure, but not between you and vendors or colleagues.
For both of you who are trying to get a hold of me, you now have the ground rules. Your mileage may vary