Hi Dan,
Yes, this is a requirement to use this "pretty cool' feature;
Managing Voice-Recognition Features (Press-or-Say Phone Input Style)
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Voice-recognition features allow subscribers to interact with Cisco Unity by speaking rather than by using the phone keypad. The features are licensed by number of concurrent sessions, and require installation and configuration of voice-recognition software on a separate and dedicated server. Voice recognition is not available to outside callers.
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/administration/guide/ex/5xcusag165e.html#wp1054336
Hope this helps!
Rob
