As of March, 2011, the Windows Mobile cumulative update for daylight saving time (DST) December 2009 is the latest DST update for Windows Mobile-based devices (versions 6.5 and lower). Any changes made to the normal schedule of DST transition times included in the December 2009 update may not be reflected accurately in these Windows Mobile-based devices. Effectively, there may be an overlap period for some time zones when the transition into and out of DST are not accurate. In some instances, the time on the device may be incorrect by the amount of the current DST offset, usually 1 hour, during this period. A current list of new / modified time zone information (TZI) keys is included in Microsoft KB article 914387.
The required updates to the time zone tables have not been implemented or tested.
Depending on the functionality provided by your mobile operator, your phone may automatically adjust its time based on the mobile operator’s network. Customers in impacted regions are advised to consult with their mobile operator regarding this functionality. Customers may still need to manually advance or regress the time setting if the device does not automatically adjust during normal operation or in cases where the device adjusts the time inappropriately. In most cases this manual change will need to occur twice: once at the beginning of the overlap period and again at the end.
Microsoft will not be providing any further scheduled updates for daylight saving time (DST) for Microsoft Windows Mobile based devices (versions 6.5 and lower). It is expected that the time information provided by the Mobile operator’s via their network is sufficient to provide the necessary transitions for these devices.