When Skype for Business or Lync are running on-premise and on-premise Active Directory is synchronised with Azure Active Directory the provisioning process needs a few extra steps.
Take a backup of your on-premise Skype for Business or Lync attributes. In particular you want to dump the User Principal Name and msRTCSIP-Line attributes.
You can do this from PowerShell on your Skype for Business or Lync server with:
Get-CsUser | Select-Object Identity,LineURI
These are helpful if you need to roll back to on-premise.
For Vorco to be able to provision your cloud identities with phone numbers, you'll need to clear the msRTCSIP-Line attribute on-premise then kick off a directory sync. Vorco will then do standard user setup on Teams. After this, inbound calls should work to Teams, but outbound won't be possible as users won't have a dial pad yet.
When you are satisfied that Teams provisioning is done and it is time to go live, you need to:
Set Teams Upgrade to Teams only. This causes Auto Attendant, Call Queues and Voicemail to work.
Run Disable-CsUser against your on-premise users. This causes the dial pad to appear in the Teams client. Do a directory sync after this.
Check there are no msRTCSIP-* attributes left on-premise. It is possible to sync and control these from on-premise if you have technical expertise but Vorco cannot assist you if this is the case so for smaller organisations it is best to let these attributes be managed entirely from the cloud.