I've determined that there's a hierarchy of communication methods.  It goes like this: 

1. Face-to-face.  This is the best method of communication.  It's what you use when you need something right away.  It's effective at getting things done, but it takes time and effort.
2. Phone.  You use the phone when it's something important but you don't want to go through as many of the normal social interaction guidelines such as greetings, how are things, nice weather, how's your wife, etc.
3. Text message.  This is probably the most efficient method of communication.  It requires very little time or effort, and it often gets a quick answer.  But it's completely dependent on the person (a) having a cell phone, (b) turning it on, and (c) having it with them.
4. Email.  This is sadly the most ineffective method of communication most of the time.  It's a great way of getting things done, but it often depends solely on the receiver, the frequency of checking, and the typical speediness of replies.

I've found several times recently that a complex problem had a simple solution, all because of a phone call.  Instead of emailing or text messaging, the problem was solved immediately by picking up the phone.  However, sometimes phone calls are ineffective because people aren't near their phone.  In that case, text messages are also usually worthless.  Emailing can be the best bet, but it depends on the time of the day and which address is used.  For example, if I email Wendy's personal address, I know she only checks it once or twice a day, so she probably won't be responding very quickly.  If I instead email her work address, it'll automatically get sent to her Blackberry, where she usually gives an instantaneous response.  However, I also have to keep in mind that emails I send to Wendy's work address occasionally get lost, so it's not always reliable. 

In conclusion, it's almost like there's a separate hierarchy of communication methods for each individual person.  I recommend not communicating at all.