Would you believe me if I told you there was an almost surefire way to get your ex intrigued enough by a message left on his voicemail, that he'd virtually beat a path to his phone to call you back? While that may be a little over dramatic to say it that way, it's the honest truth...there are things you can do in the messages you leave him that will implant you so in his mind that he'll almost not be able to help calling you back!
There are two special triggers for the human mind that will provoke your interest to the point where you almost can't think about anything else. If you can "flip these switches" you're all but guaranteed a response to your message...these two triggers are Self-interest and Curiosity.
If you want your ex to call you back, all you need to do is appeal to his self interest and curiosity. You'd be surprised how simply and easily this can be done, as in the following example:
"Hey John, it's me Katie. Listen, I just wanted to thank you for what you did for me...it really helped me out, and if you'd call me back I'd really like to thank you in person."
Something as simple as that can be as powerful as if you just turned a knob in your ex's head and set him to Interested mode. By appealing to both his self-interest (what did he do?) and his curiosity (again...what was it he did?), you're targeting the two most powerful interest triggers in the human mind...drop one of those bombs on his voicemail, and it won't be long before you get a call back.