My customer will not return my calls.
Unless you know your customer very well and have an excellent relationship with them, they are unlikely to return your calls without a good reason. Just leaving your name and number is not going to work. People in businesses who have the authority to buy your solutions are likely to be busy and without a compelling reason, are not going to call you back. You need to give them a reason for them to spend the time calling you.
If you are going to leave a voice mail for them, much preferable to a colleague taking a message, then give them a reason to call you back. Try to hook them with some useful information or a bold claim about what you can do for their business. Make them intrigued about what you have to offer so that they want to call you back to find out more.
Once you have left your message, leave it for a couple of days before you try again. If they call you, then it tells you that you that there is definite interest in your solution which is very valuable information as you proceed with the opportunity. If they don't call back, it doesn't mean that they are not interested, they may have been extremely busy or out of the office. Try calling again but don't bother leaving a message. They don't need to hear what you have to say three or four times. If it didn't work the first time, it probably wont work the fourth time!
Two of our training modules may help: