The customer sends his request by e-mail.
The agent knows the phone number and he replies by phone to get some further information.
The agent sets the ticket on "waiting" because the customer has to provide some further information after the cal.
Issue in this case
The SLA [first reply time] does not count this call as first reply and it does not stop.
Actual the first reply has to be a public comment.
The SLA [first reply time] has to consider that agents can also call the customer.
Calls should count as first reply action.