Here in the U.S., as well as in a few other countries I believe, we’re extending Daylight Savings Time this year by roughly four weeks over the current standard. Microsoft has some documentation on the impact to your Windows Mobile handheld and one kind soul created a CAB file to address the issue. If you’d rather not run the CAB he created, you can create your own using the info on the Microsoft page.
Ideally, your Windows Mobile handheld OEM or your phone carrier (if you have a Smartphone or Phone Edition device) should be providing a fix based off of the Microsoft code. It might make sense to wait and see if that happens, but if not, you’ve got this as a backup plan. I suspect that phone devices will a clock reset via the airwaves, but there could still be impacts to the Time Zone settings and appointments in your calendar.