Make a Guest Call from the Lifesize app You can call Lifesize users even if you do not have a Lifesize account. You can also join a call from a non-Lifesize conference room system. Download the Lifesize app. Open the Lifesize app and click I am a guest Enter your name and the number of the person you want to call. The number uses this format: email@example.com. Click Next. Lifesize users, learn how to call someone.