Just today I had a location that started getting crummy VoIP quality. Guess how I found out? Yeah, my client had to call me! I hate that! So I started looking for a MOS VoIP quality monitor web service and VoIPspear showed up. They have a free version that will show you a chart of your MOS quality for last 6 hours. Or for $1 a month they will send an email. Check them out at http://www.voipspear.com and let me know what you think of them. Or if you know a better service, please let a comment.
Quality VoIPing fellows!