If you use a new Linksys VoIP phone (for example, the Linksys SPA942), you probably don't have to worry about the change to Daylight Savings Time that began in 2007. By default, your phone has the right information about when Daylight Savings Time begins and ends.
On the other hand, if you use an older phone or adapter (such as the Linksys SPA2100), you might have a problem. Older models do not have the proper start and end times set by default. In order to fix this, you need to put the following text in the Daylight Saving Time Rule field of the Regional tab under Voice:
If you configure your phone via a remote provisioning method (TFTP, HTTP) and XML, you'll need to add or update the following:
This setting (along with Time Zone) affect the time displayed on your system and in Caller*ID. Therefore, it pays to get it right!
UPDATE: This setting appears to not take effect unless you have an NTP server configured on the device. So, make sure you assign a primary NTP server.