I prefer to use email for most communications as it makes it a whole lot easier to pull up past conversations. If I'd had communication in the form of calls, texts, IM's (probably on multiple clients) as well as email, it'd probably be more difficult to pull up any information that I may need later on.
Using email alone allows me to search for specific conversations, and not have the trouble of losing or having great difficulty finding conversations.
I do occasionally use Skype and IRC, but I know which people I communicate with on these platforms, and keep on top of documenting anything I may later need to refer to.
I agree that if you need something urgently, then a call can be great. However, for general communication, I see no issue with using email.
I think it'd be a more interesting topic to discuss how to efficiently use subject headings, as I've often had important emails slip under the radar, and less important emails demand some form of urgency that isn't existent.