This is one that a lot of people have asked for. It looks like Microsoft is very cautious about giving out the OneCare tech support number, rather opting to make you jump through a variety of “online help” tutorials.
You can contact OneCare support here:
Help Site: help.live.com
Phone: 1-866-ONECARE (1–866-663-2273)
If anyone has any email addresses send them to me and I’ll add them to this page.