Wait, I would say MSFT had a decent mobile OS (relatively) from 2001-2007. I remember at the first iPhone (iOS 1), WM2005 had far more functionality (etc. GPS, apps, handwriting support). WM was better than PalmOS because I moved from the Palm m505 over to the HP iPaq 1910 and then to the GPS iPaq smartphone (don't remember the model number). iPhone didn't get gps support until the iPhone 3G.
So MSFT only screwed up the last 10 years of mobile development. It's the tortoise and hare problem. MSFT exceeded features and crushed the existing competitions (Palm, Netscape, Lotus, WordPerfect) and then sat around getting pass by new competitions (iOS, Android, Chrome).