Skype, probably the biggest non-SIP voip provider in the world, violates GPLv2, the open source license. The software itself is fine, but one of the SMC phones they sell through their site runs linux. The source code was not provided, as stated in GPLv2.

Skype did, however, issue a flyer that contained URLs to the GPL license and to the source code. The GPL only permits a URL for software that is delivered over the internet.(TheRegister)

I happen to own this phone (although not bought from Skype), and indeed, I never received the source code either.
Nothing that will shake the world. Skype has been convicted of the crime by a german court after complaints of Netfilter developer Harald Welte, who also runs gpl-violations.org. The punishment will fit the crime - a small fine will be issued.