I am planning to deploy 4 small sites (50 to 65 users each) and interconnect them for IP telephony.
What came in my mind was to use ISR routers with CCME software on each site and provide unity for voice mail feature as well, on each site.
The only problem I am having is how all the sites will be able to communicate ? does CCME routers registers between each other and keep a centralized database of all the users of the 4 sites ? That would be great for me as I want a user going from site 1 to site 2 to be able to just connect its laptop and gets its number and environnement like he was at his location (using a softphone installed on his laptop)....
Any hint about this design would be helpful as I am quite new in Cisco IP Telephony.
Can someone suggest another simple way to have a design to solve problem of :
1- mobility of users between sites (they can keep their existing environment)
2- survivability of a site when connection to the other site is lost (users of the same site can call each other)