The toll free number can't be posted, and you need to have an active subscription to authenticate to get the number per the information here:
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
Unofficial path - send me an email at sboots@mvps.org with a subject line including "OneCare" (to get past my spam filtering) and in the message body, tell me what country you are in, your forum nickname, and paste this link:
http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/bdfb3ce5-82e8-4262-9162-ef6b0c9e58dc
I am not online 24x7, so you may be waiting for a reply, but I'll do my best to hook you up with support.
What problem are you having with the installation?
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator