Cisco has been in the voice game for a while now and is now the #1 IP PBX vendor in the world. There is literally thousands of features rolled up in the Cisco voice solutions portfolio. Sifting through them can be quite a challenge. Below are the features that I consider to be "game changers". I define a game changer as being a feature that is not current requirement by the organization but would considerably change the way the organization works in positive way effecting users to be more productive and offer better service/responsiveness.
MeetMe Conferencing: This enables a user to setup his own conference bridge to host a voice conference. Participants then dial in directly from either inside or outside the firm. This can provide significant cost savings as most firms can easily spend $500-$1,000 in conferencing monthly.
Single Number Reach (aka Voice Connect): Rings the desk phone and cell phone simultaneously. The call can be picked up on either and passed back and forth seamlessly. This feature can be controlled with access lists and schedules to control what calls reach the mobile number. The original caller id is preserved so that you know who is calling even on your mobile phone.
Voicemail transcription (aka SpeechView): Typically users receive a copy of their voicemail via email to their smartphone, however, there is no way to tell if it is important or not unless they listen to the message. This feature sends a voicemail with the voicemail transcribed in the message with the voicemail as an attachment. This is especially valuable when the user is not in a position to listen to voicemail but might be able to read a message on their smartphone.
WebEx Connect: This is a small application that is licensed on a per user basis and is a SAAS offering from WebEx. It provides instant messaging, desktop sharing, click to call, and can even be used to start a WebEx Meeting. Advanced configuration also allows it to function as a softphone. This service can be federated meaning that it can be used to connect to other instant messaging clients. Auditing can be configured to address security concerns.
UC Phone Proxy: This feature enables users to connect a Cisco ip phone to any internet connection and register the phone securely with the CCM/CME. Calls are encrypted for security. Takes less than 5 minutes to provision on the administrative end and gives new meaning to "home is where you hang your hat". Very valuable for execs and mobile users or contractors that setup shop temporarily in foreign offices. (Cisco ASA required)
Personalized Auto Attendant: Voicemail boxes can be configured to support caller input so that a caller might have the option to reach an administrative assistant directly.