If you already have Cisco Expressway MRA and SIP URI dialing activated in your Cisco Unified Communications environment, then you should seriously begin to think about activating another very key feature within Cisco Expressway: Business-to-Business dialing.
This feature will bring your collaboration with your partners and customers to whole new level; allowing you to have audio and video calls with them as seamlessly as you do with your coworkers.
A big part of the configuration process for B2B calls is deploying public DNS SRV records that will allow your partners and clients to call you using your corporate domain.
Assuming you have all necessary ports on the firewall already opened. The following will take you through the steps required to effectively configure the B2B SIP URI dialing feature within Expressway.