Microsoft is preparing 2 major upgrades to Windows Mobile, one has code name Windows Mobile Crossbow (based still on Windows CE 5) and the other one has code name Windows Mobile Photon (based on new Windows CE 6).
Windows Mobile 5 is the current OS of choice for Windows Mobile users however the next iteration, codenamed Crossbow, has shown its face. It has a glossy title bar and soft keys and will feature Vista-esque folder icons etc.
Pieter Knook, a Microsoft Sr. VP, has commented that Microsoft plan to release an upgrade to their mobile platform yearly which is interesting and could mean a new OS with every yearly upgrade for pay monthly contracts. Knook has also commented that Crossbow will have strong links with Office 2007 and Exchange 12 as well as including the mobile version of Office Communicator, an Instant Messenger tool for enterprises.
Google cache caught a leaked presentation which told us that Crossbow will be released to manufacturer in Q4 2006 ready for release in Q1/Q2 of 2007 and that the next operating system (codenamed Photon) will be released to manufacturers in Q4 2007 ready for release in Q1/Q2 2008 (Photon is set to include a new, flexible shell with modular containers and utilise the "Yamazaki" CE kernel).
News source: MobileTopSoft