As we line up each of these communication tools, we can see that many of them will evolve beyond their communication purposes. Foundry Group Blog, for example, talks about email and says how it can evolved to social networks and know management. Personally, I have also used Twitter as a news aggregator by reading the links of those I followed, although I do not have a Twitter account.
As these different purposes evolve, I believe there will be opportunities for startups to build applications that integrate with these communication platforms. Xobni for example has a great product revealing your email's social network to the user.
So what I have done below is to map out the communications platforms vs the different purposes they can evolve to. This is a work in progress. I will trying to fill the names in the coming weeks to see if there are any more opportunities left!