Microsoft are offering free Audio Conferencing license for a year and a discount for Advance Communications licenses. Also FastTrack support for moving off Skype for Business users.

More information is available on Microsoft website at: https://www.microsoft.com/en-us/microsoft-365/blog/2020/09/08/3-deals-meeting-calling-experiences-microsoft-teams/ 

Very useful if you do not already pay for the licenses.