According to this press release: Liz Claiborne Inc. Receives Cisco's 4 Millionth IP Telephone, Cisco Systems (NASDAQ:CSCO - News) today announced the sale of its 4 millionth Cisco Internet Protocol (IP) telephone to fashion apparel and accessories icon Liz Claiborne Inc., a milestone that demonstrates Cisco's continuing acceleration in the enterprise voice market. "It took us 4-and-a-half years to sell our first 2 million IP phones and only 14 months to climb from 2 million to 4 million phones sold to customers," said Barry O’Sullivan, vice president and general manager for Cisco's IP Communications Business Unit. "The 4 million milestone that we achieved in October this year, confirms our leadership in the enterprise voice market and demonstrates the rapid market acceleration we are driving in this space. It also points to growing customer adoption of our IP Communications system."

More proof of the "hockey stick" exponential growth curve of VoIP. VoIP got off to a slow start slow, but that curve is hooking straight up now!