When you place a customer on hold you have two options, dead silence or some form of music or promotions. With nothing to listen to each second will seem like minutes to your customer. Listening to music on hold will help pass the time. While your customer is on hold they are a captive audience whose attention could be focused on your business or products with promotions on hold. SoundTel offers a variety of music and promotion on hold systems.
Have a look at the Nel Tech Labs SoundBrick® 550 : 
Seattle area top provider of telecommunication since 1984 