You have to investigate the office to find clues about whom to call, then use the numeric keypad to manually enter the phone numbers. Once you're on the phone with someone, you have to decide what to say. It's also important to first choose the voice you want to use, since you can only get certain information if you choose the right voice.
Supercontinent Ltd is an outstanding graphic adventure with an awesome atmosphere, an entertaining story, and some really original puzzles. Yet another fantastic game from Deconstructeam, developers of the no less brilliant Gods Will Be Watching.