In August 2003 Swedish entrepreneurs Niklas Zennström, Janus Friis, and the Estonians Ahti Heinla, Priit Kasesalu launched the peer-to-peer voice over Internet Protocol (VOIP) telephony service, Skype. The name of the company evolved from "Sky peer-to-peer" or "Skyper." However some of the domain names associated with "Skyper" were already taken, so the final "r" was dropped leaving "Skype," for which domain names were available. Skype was sold to eBay, based in San Jose, California, in September 2005. On 10 May 2011 Microsoft purchased Skype from eBay for a supposed $8.5 billion. According to the Wikipedia Skype had 663 million registered users in September 2011.