Software licenses allow you to unlock features on a device or, for example, expand support. Virtually every device offers this option. For example, on ARGUS testers, you can use them to unlock features like internet speed testing, or on Spectralink DECT servers, you can expand your user base or activate (new) functionality.
For Yeastar central units, you can purchase and/or renew the Cloud version or Linkus client software.