I have been using Trixbox CE for a couple of years and a client has asked me to setup a VOIP system with two phones and a couple of extensions. When he gets hit with a borage of phone calls I need to have the call that are behind the others to go the the next extension. I need redundancy if one Internet connection goes down and have the another kick in or failover. How does one configure Trixbox to failover to the other Internet connection and can someone give me a list of carriers in the Washington D.C area. Can someone point me in the right direction?

Are you looking for traditional pots/pstn/voip carriers? If you're talking voip... there are literally hundreds and hundreds who service the DC area.

VOIP carriers, I guess I would need a DUAL WAN router and have two different carriers with separate circuits in case on goes down.

Generally with voip carriers you get your own internet connectivity then connect to their sip server over it. If the site needs internet connectivity too you'll need to figure that before looking at getting voip.