You CANNOT delete your account, and they are quite clear about it.
For more info, see: http://support.oovoo.com/link/portal/3908/4244/Article/576/How-do-I-cancel-or-deactivate-my-account
URLS:
http://oovoo.com
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.