The plug-ins require that the user is licensed for Sametime Standard. But the plug-ins themselves are free. So if you have Cisco telephony and a Lotus Notes environment today, you really should be looking at deploying them for your end-users. The only additional hardware you might need to deploy and license would be a Cisco Presence server, and that is only if you want the phone presence to be displayed.
Here is the video on the Cisco voicemail integration.
And here is the video on the Cisco phone control integration.