-How well do you know the person.
-How important is this task, decision or event?
-How complex is the task, decision or event?
Meeting<---------------------------------------->Email
Don't know person well--------------------Know person well
Important---------------------------------Unimportant
Complex-----------------------------------Simple
If I don't know someone well they are more likely to misinterpret raw text (flame wars are a good example.) If something is unimportant then it doesn't matter if they misinterpret raw text. If something is simple then there is less to misinterpret.
E-mail is for presenting an case, making a conclusion, and asking for agreement. It's a longer format where you get a chance to speak in a one-way fashion.
The phone is great for immediate decision-making: the server is down and I need to know whether to ring the alarm bell or not. With the phone you can get a lot out of voice inflection that you can't get with IM or email. In general, written format is very tough to do humor, nuance, sarcasm, and negotiation.
BTW, the term "meeting" is way overrated. If you're doing work in a group, do the work, whether it's at the water cooler, Starbucks, whatever. There's a whole science involved in making a good meeting, but I'd just focus on the work and make the communication format fit the goal. Use common sense. You obviously can't make a marketing strategy using IM, email, or twitter, so some kind of meeting/workgroup is in order. Likeise, if you've stopped five people working to tell them the code just built, you need to do a little thinking about choosing better formats.