You should be able to do this via the conditions field in the rules module. Unsure how to create an 'are you sure' option, but you could certainly stop them from doing it with rules.
There might be better solutions, but here's what I'd do if I wanted to achieve what you are doing.
Install Flags and Rules module. Create flag to appear on Content Type 'Phone call' called 'Delete this call'.
In rules create two rules. One called Delete call, the other called 'display message about unable to delete call'.
Triggered on action - node is flagged
Conditions - Entity has field call date/time (whatever the field is called)
- Data comparison - select the date/time field, then is greater than +1 minute.
Then action - unpublish content
For the second rule do the same but change second condition to less than - 1 minute. Then as the action do 'display message on the site' and select message as 'Unable to delete calls that have passed'.
That should work.