Music On Hold
Music is better
Most callers will hang up within a minute if there's only silence on the line. FortiVoice indicates that the line hasn't died with a default on hold beeping tone. Better yet, you can upload an audio file to play back to callers while on hold.
You're not limited to music, either. You can use any sound recording you want, including advertisements or information about your company or products. You've got a captive audience; sell yourself!