According to the Gartner data reported in this Computerworld blog item…
iPhone browsing marketshare closes in on .1%
… the iPhone browser marketshare eclipsed the total Windows Mobile browser marketshare in less than half a year. That is pretty impressive considering that Windows CE/Windows Mobile has been around since late 1996. The iPhone checks in with 0.09% of the browser market share while Windows CE (aka Windows Mobile plus a few other devices) had a 0.06% share. Something listed as simply iPod in the list is probably the iPod touch and has a 0.01% share. If you add that to the iPhone, it has a full 0.10% browser share. I guess this explains why so many sites are building iPhone tuned web pages. The iPhone clearly has momentum in the mobile browsing world.
Other points of interest: The Nokia S60 series has a 0.01% share (same as the iPod touch). The Hiptop shows up with 0.02%. Windows XP is #1 with a 78.37% share. And, Windows Vista is a distant second with a 9.19% share. The Mac is divided into two categories: MacIntel (3.59%) and Mac OS (presumably PowerPC based with 3.22%) with a combined share of 6.81%.