Dan Paulson has joined Signal Technology Corporation as vice president of mobile appliance sales and marketing. He will be responsible for marketing and development strategies for Signal's entry into the market for advanced semiconductor modules for next-generation mobile phones and wireless appliances.   . . .   IDT has appointed Gregory Lang as its new president. IDT's current president and CEO, Jerry Taylor, will continue to serve as CEO. As president, Lang will oversee all product businesses, technology, marketing and sales functions. Taylor will continue to maintain responsibility for manufacturing, as well as finance and administration.   . . .   Real Estate Opportunities Inc. announced it will locate its development and production facilities for PocketSpec Technologies Inc. in the Denver area. Real Estate Opportunities Inc. acquired the technology for the PocketSpec Color Analyzer from Color-Spec Technologies Inc. in September and is in the process of changing its name to PocketSpec Technologies Inc.