It's not nice to badger people. That's why you have business rules. You want to make sure that nobody gets called more than a certain number of times in a given span. If somebody is "Busy", you want to call them back soon. If the number is "No Answer", you should wait at least a certain amount of time before trying them again. Don't hammer your contacts.
It's great to have software that does that automatically for you. That's why we built it into the VitalVox Hosted Call Center ACD.