The Register is reporting that British Telecom is now attacking the VoIP industry by claiming that it has patents over the IETF standardised Session Initition Protocol (SIP RFC 3261)
SIP is widely implemented in free software, in standalone products such as Lumicall and in Linux distributions such as Debian that carry a wide variety of SIP servers, SIP proxies and SIP clients, including the default chat client Empathy
It remains to be seen whether they will engage in a similar attack on related protocols like XMPP / Jabber
Many of the VoIP companies under attack are heavy users of free software