I did this once with 'Blue's Professional' from Imagicle.
This is a callaccounting tool. Nice and not expensive.
One feature is, it can send 'Alarm' E-mails when certain criteria is met. Like calls to strange destinations, long duration, ect. And one criteria is unanswered calls. It will sent one mail per 5 minutes.
They have a simple huntgroup for the sales number. If they could not answer one or more calls, then they get a mail with a list of numbers trying to call during the last 5 minutes. As soon as the can, they call everyone back.