AIM. I think this should be the standard. Whenever I see someone who's providing a service (SEO, design, etc.) and they only have MSN, Yahoo Messenger, or whatever but no AIM, that's usually enough for me not to work with them. Take note, I'm not the only one that feels that way.
Huh? AIM? Really? I'd say skype..
wtf is so special about AIM you guys??