This is really shiny!
Yahoo definitely gets it! Wonder if this would work on my wife's Nokia. While unlimited texting has surprisingly been tri-telco nowadays (thanks to Sun), applications that leverages the power of the Internet and combine it with richer UI's is definitely the way to go. Instant messaging via your mobile phone is quickly changing the way we communicate. SMS, primarily due to costs is currently suited mostly for local messaging. Instant Messaging (IM) on the other hand, can cross bounaries and is available across different devices (from PC's, PDA's, cellphones etc).
As data connection costs becomes less of an issue, this can also bring forth the rise of mobile web browser based applications which quite blends well with Sun's the network is the computer slogan. Meaning it won't matter much if your phone's processor isn't bleeding edge, manufacturers might as well focus on making better displays to accomodate mobile content. Mobile flash comes into mind, as well as AJAX, and a whole lot more! limited only by your imagination.
We live in exciting mobile times!