Remember NTP? They're back -- with a slew of lawsuits against some big name mobile operators.

The holding company that brought the BlackBerry Nation to its knees in 2006 is once again on the advance, this time filing suit against AT&T, Verizon, Sprint and T-Mobile. The suit was filed last week in Richmond, Va., home to the last round of legal tussling between NTP and Research In Motion, maker of the BlackBerry.

In 2002, NTP won a jury verdict that RIM infringed on patents held by the late Thomas Campana for a wireless e-mail system. RIM tried several times to overturn that verdict on appeal but never prevailed, and in March 2006 the companies settled for US$612.5 million.

The settlement came despite the fact that the US Patent and Trademark Office issued final office actions invalidating most of NTP's patents at issue in the case. NTP is appealing that decision, in a process that could stretch on for years.

Now, NTP is going after mobile carriers. Eight patents are cited, five of which were argued in the RIM litigation. The argument this time seems to be that because hardware makers like RIM and Nokia have licensed the patents in question from NTP, the carriers should have to have a licence as well. NTP wants ongoing royalties as well as damages from the carriers.

Craig Merritt, a lawyer with Christian & Barton in Richmond who is representing NTP, did not immediately return a call seeking comment on his client's current thinking with regard to its patents and the wireless carriers.

Campana, who died in 2004, was issued several patents for a wireless e-mail system but never brought a product to market. NTP, the company formed to enforce those patents, has also sued Palm in a case that has been stayed pending the PTO re-examination process.

A call to the US Patent and Trademark Office seeking an update on the re-examination process was not immediately returned. Patents are often re-examined at the request of the patent holder as a way of receiving a confirmation that the patents are valid before asserting them at trial. But the PTO and RIM initiated re-examination hearings in 2005 with the belief that the patents in question were invalid. The initial finding of the PTO (called a final office action) was that the patents were invalid because of prior art.

However, that's a preliminary decision. NTP can appeal those decisions to an appeals board at the PTO, and then to the U.S. Court of Appeals for the Federal Circuit, where NTP has prevailed already in the RIM case. And if NTP manages to secure a jury verdict in its favor before the patents are formally invalidated, the wireless carriers would still be on the hook for whatever damages are awarded by the jury.

Tom Krazit writes for CNET News.com

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