I'm looking for a way to schedule a call with one contact and associate the same call with another contact. Typically, I would imagine this can be done by using the "Related to" Field in the call. But I can't find the option to associate a contact here in the drop down. Please help.

example - if I call one contact who is a vendor to talk about the status of another contact's service delivery, etc.

I understand that for most companies this would be related to a particular deal, or perhaps even an account. But in my case it is more relevant to mark another contact - or sometimes even a lead - in "Related To". If there is a way to do this already, please let me know.