for better quality of service with current bandwidth you are using, use Asterisk/SIP Server which is completed with the best audio/video codec installed within. There are several free pbx server you can use: AsteriskNow, Elastix, or Trixbox. So, each customer will be linked over SIP connection. This will make you save bandwidth in a lot, but the quality is the best. I ever did some small research with this method, and the result is incredible. Let me know if you are interested.