Everybody's favorite patent troll, NTP, is back. It, of course, was the company that managed to wring $612.5 million out of RIM, maker of the BlackBerry, for patent infringement -- despite the patents in question being on their way to being rejected by the USPTO after a bunch of prior art came to light. NTP has now sued AT&T, Verizon and Sprint, as well as T-Mobile, for infringing on the same patents. RIM's settlement with NTP was widely believed to protect its carrier customers from infringement suits, but it's likely such protection extended only to their use of RIM products, not other mobile email systems. It's not too surprising that NTP sued, since it's a patent troll and that's what they do, though it's slightly curious since the suits were filed in the same Virginia court, with the same judge, as its previous cases. This includes its earlier suit against Palm, which the judge put on hold until after the validity of NTP's patents is finally assessed. It's likely the same thing will happen here, but NTP probably doesn't care too much -- it's just looking for more leverage to wring undeserved settlements and licensing deals out of anybody it can.