How to report contacts that have received an email but haven't received a follow-up phone call?

How to report contacts that have received an email but haven't received a follow-up phone call?

We have a simple marketing campaign where we are sending out introductory e-mails to be followed up by a phone call.  How do I generate a view or report that shows people to whom we have sent emails that need a follow-up phone call?
 
Any help greatly appreciated.