Bloomberg said that Sprint has launched legal action against Time Warner Cable, Comcast, Cable One and Cox Communications alleging infringement of patents related to the provision of voice services over digital lines.

Some of the companies involved have a close relationship with Sprint, with Time Warner Cable and Comcast also being shareholders in Clearwire, the majority Sprint-owned wholesale mobile broadband provider.

Time Warner and Comcast are also part owners of a consortium that recently announced a US$3.6 billion sale of spectrum licences to Verizon Wireless, alongside peer Bright House Networks.  This deal will also see the companies working together in a service partnership.

Separately, Reuters said that this transaction is set to be investigated by the US Department of Justice, with a particular focus on the fact that the companies involved have opted not to use  the spectrum themselves to provide services – removing potential new competitors from the market.

The patents asserted by Sprint against the cable companies include the same intellectual property that Sprint previously said VoIP company Vonage had infringed, which saw Vonage inking a multi-million dollar licensing agreement with Sprint after a 2007 trial, Bloomberg said.

The cable companies have declined to comment on the pending litigation.

Some observers noted that the timing of the action, following the defendants’ deal with Verizon Wireless for spectrum and services, seems too neat to be purely coincidental.