If you know someone who uses Skype for Business or older versions of Lync in another organisation, you can federate with them and use Skype for Business to communicate just as you do with your colleagues. In order to get this working, you will need to ask the other company’s IT department to add VIA as a Hosting Provider in their Skype for Business or Lync 2010/2013 environment.
Run the following command in a Lync Server Management Shell console:
New-CsHostingProvider -Identity VIA -ProxyFqdn “sip.lync.unifiedcaas.net” -Enabled $True -VerificationLevel UseSourceVerification
You will need to be a member of the RTCUniversalServerAdmins group to run this command.
Skype for Business Online Federation
Skype for Business Online federation does not require any special configuration to federate with a hosted domain.
Make sure the Skype for Business Online users have “allow federation with” – “all except blocked domains” set in the Skype for Business Online control panel.