I work for a medium-sized business by most estimates (~6k employees).  To me, unified communications is the bridging of all different means of communication into one, single, logical system.  That means voicemail, email instant messaging, pots, etc. ...

I'd recommend using a cisco 2509-2512:http://www.cisco.com/en/US/tech/tk801/tk36/technologies_configuration_example09186a008014f8e7.shtml