After making IE9 available in the desktop, the browser will make it onto the phone .. but I can't disclose the timeline on how soon after we release because we don't yet know it, rest assured we do want to have HTML5 in the phone and will do our best to get it in as soon as we can; we will have to see how schedules align next year.
I think you not only need to invest in the browser, but you probably need to rethink how IE development is managed between desktop and mobile. It doesn't make sense anymore for the IE team to be part of the desktop Windows division, develop for Windows, and only later port to mobile (how I understand it to work currently, correct me if I'm wrong). Mobile should be a priority from the beginning. If anything mobile IE is a lot more important than desktop IE as there are plenty of other browsers on desktop Windows, while Windows Phone, being a minority platform, benefits more from access to a rich standards-based application base to protect against everyone getting locked in to iPhone or Android-exclusive apps.