Basically there are two Client licenses that are additative. You always need a Standard CAL and can on top of that buy an Enterprise CAL that deliveres all of the Conferencing (Web, Audio/Video, Application Sharing) and the VoIP & Remote Call Control features.
For the servers there's the Standard and Enterprise Edition (Scalability and Availability) and you should note that Communicator Web Access, Speech Server 2007 and Office Communicator Mobile 2007 are included in the server licensec.
Update - find more information on licensing options on the web page How to buy Microsoft Office Communications Server 2007.
For pricing information according to Michael Dunn's posting regarding Speech Server 2007 pricing it will be -
- Standard Server - $699.00
- Enterprise Edition Server - $3,999
- Standard Client Access Licence - $31
- Enterprise Client Access License - $139
No info from Dunn though on the licensing type / price (MVLS, Select etc.)