Following up with people who did NOT schedule

I've never followed up with people who called and didn't schedule because if they didn't schedule I didn't get any of their info and I feel I've been missing out on potential work.

Now I've got an answering service answering my phones and they do an excellent job of recording the name, phone number and the services the customer asked about and even emails from the people who will give them out even if the person does not end up ultimately scheduling with me.

If there is anyone doing this I'd...

Following up with people who did NOT schedule