You have the right answer. Busy. Never give up on me. If the answer machine takes your message I'll return your call if I can understand your phone number. Too many people say it too fast to be understood, or let their volume die off as they are completing the number.
Don't be bashfull. Leave more than one message if you don't get a call back promptly. It is rare for me to wait more than one day to return calls, and that will normally be a weekend.
