On many phones, mobile instant messaging = text messaging. The OZ Instant Messenger included on Windows Mobile devices from AT&T and T-Mobile uses SMS for delivering IMs. A lot of other dumb phones also use SMS for IM. So in many cases, it's the same thing. I think text messaging and instant...

Personally I love IM. ..but I don't think people have the IM-mindset when they are not infront of their computer... yet! And I have to say the Windows Live client on Windows Mobile suck. It's wasting screen space with the huge tab bar, too power consuming and the contact syncronisation does not...