The Better Than Leaving a Message Technique

Instead of leaving a message for a Hiring Manager (who may have no idea who you are), it may be better to reply:

"I may be difficult to reach today. Could you give me a time when it would be best to reach _____?"

Then let the person know you will call back and ask if they would please let the Hiring Manager know you will be calling at that time. You are much more likely to get through.