Dr. Pamela Takayoshi, Associate Professor of English at Kent State University, is claiming that IM speak is not just slang but represents a whole other language, separate from English. From the press release:

Instant messaging, or IM, is not just bad grammar or a bunch of mistakes. IM is a separate language form from formal English and has a common set of language features and standards.

While I agree that when you understand the rules of IM speak there is some standardization to it, it is still at its root IM based on English words. I think this becomes a semantical debate as to what constitutes a language. I'd accept that IM speak is a separate and unique dialect of English, but I'm not sure it qualifies as its own unique language. I'm willing to be persuaded otherwise, though.