It’s not yet possible to use a Threema ID on multiple mobile devices at the same time. You can, however, use the desktop app or the web client to connect to the device on which your Threema ID is set up.
A multi-device solution that meets Threema’s strict security and privacy requirements is currently in development. A beta version of the upcoming desktop app is already available, and it can be used even if the associated device happens to be offline.
