That's yet another one of the projects on my ToDo list, which stretches around the corner of my house and out past the driveway. I thought for certain after I bought the Treo 600 I would find time to set up a moblog, but it has not yet come to pass.
I've look at two free (for now) hosted sites, but haven't tried either one.
TextAmerica - http://textamerica.com/
MoblogUK - http://moblg.net/
There's some useful article in an article from last November at The Feature (http://www.thefeature.com/article?articleid=100193). There's also some good info at http://www.moblogging.org/.
Although I assume you are interested in camera-based moblogging, if you're interested in audioblogging you might want to check out a tool I wrote called PhoneBlogger. It was the first publicly available tool to let you audio blog by phone. I have to admit that it is not trivial to set up, but it is free and open source and I can obviously assure you that it will run on a DreamHost server.