You can use Cisco IP Communicator in tandem with a Cisco Unified IP Phone to place, receive, and control calls from your desktop PC. All features function in both modes of operation.
The Cisco IP SoftPhone and IP Communicator are a PC based IP Telephony endpoint that offers the ability to make a PC work like a Cisco 7900 Series phone.
User Guide for Cisco IP Communicator:
http://www.cisco.com/en/US/docs/voice_ip_comm/cipc/2_1/english/user/guide/cug21book.pdf
Preparing to Deploy Cisco IP Communicator:
http://www.cisco.com/en/US/docs/voice_ip_comm/cipc/2_0/english/administration/guide/CADnet.html