Select MSIís mainboards based on Intel P35 core-logic come with a built-in SkyTel module card paired with Realtekís ALC880T HD audio codec to enable a standard telephone to be connected to the PC, according to a news-story at DigiTimes web-site. This can be used for Skype calls as well as traditional telephone calls. The traditional phone can still operate while the system is shut off.
As the article brings out, similar devices exist in the market. This is one of a very few motherboards, however, that'll have such a feature, and could be an indication of something that may come stock on consumer-level boards in the future.