<A HREF="http://money.cnn.com/2006/02/01/technology/rim/index.htm">The Justice Department reiterated concerns</A> Wednesday over a potential shutdown of Research in Motion's BlackBerry service in the U.S., saying it remains unclear how a blackout would impact government workers. "There are still a number of serious questions to be answered as to how an injunction can be implemented so as to continue BlackBerry service for governmental and other excepted groups," the department said in a brief filed with a federal district court in Virginia. RIM is locked in a legal battle with U.S. patent holding company NTP. The case goes back to 2001, when NTP filed a suit against RIM claiming that the BlackBerry infringed on its patents. A jury found in favor of NTP and awarded the company damages.