NTP, which last year won a $612.5 million settlement from the maker of BlackBerry, has sued several wireless companies for patent infringement, according to court papers.
The lawsuits were filed on 7 September in the US District Court for the Eastern District of Virginia against Sprint Nextel, AT&T Mobility, Verizon Wireless and T-Mobile USA, according to court documents.
The patents relate to e-mail, according to the documents.
Virginia-based NTP is best known for its battle with BlackBerry-maker Research In Motion, which agreed last year to pay $612.5 million to NTP to settle a damaging and drawn-out patent infringement fight.
Spokespeople for the wireless companies were not immediately available for comment.
The Wall Street Journal earlier reported the lawsuits on its Web site. The wireless carriers all declined to comment to the Journal.
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