NTP Corporation has filed a lawsuit against six leading cell phone makers for infringing on its patents for delivering email to cell phones. The companies against whom cases were filed are Apple , Google , Microsoft , Motorola , HTC  and LG. NTP claims that the companies are infringing eight of NTP’s patents related to the delivery of email over a wireless network.

“Use of NTP’s intellectual property without a license is just plain unfair to NTP and its licensees,” said co-founder Donald E. Stout. “The filing of suit today is necessary to ensure that those companies who are infringing NTP’s patents will be required to pay a licensing fee.”

In December, the U.S. Patent and Trademark Office validated 67 of NTP’s claims in four patents in the RIM litigation and said RIM infringed three claims. NTP has won $612.5 million from BlackBerry maker Research In Motion Ltd. (RIMM, RIM.T) to settle a patent-infringement lawsuit in 2006.