We were approached to provide a Voip solution for a London Solicitors. They were moving from a Single office to two offices in different parts of the city.
At the Primary office we installed an Asterisk server that was connected to the ISDN30e link where all DDI numbers were delivered for both sites. This site also had its own VOip connection as well
At the main site the operators were based using the Asternic FlashOsPanel for displaying extension status for both sites.
A key feature of the system was to provide a flexible system for out of hours callers to contact the duty Solicitor. This was provided so that callers on calling out of hours can leave a message for the next day or press an option to contact the Duty solicitor. The Duty solicitor can call into the system and change the contact number at will if for example they are busy with a client.
A SIP trunk connected both sites together over a 20Meg link that was used for both voice and data.
The new sites were not in the exchange area of the original phone number so this was ported to Gradwell.net so that it could be delivered via an IAX2 connection to the relevent server.
The handsets used were a mixture of Aastra 53i and 55i with an xml appliction to set DND status in the Flash ops panel and light the light on the handset.