Hi Rod,
We use Teams and 8x8 with ~700 of our users odd issues here and there but as long as you remember its two seperate phones systems and apply policies to stop thing breaking it works well ( e.g. decide on VM on 8x8 or Teams, turn off teams call forward).
The main reasons for the dialer not appearing is either MS license or left over attributes in Azure AD for Skype for Business etc. I presume you use Azure AD connector you need to clear these attributes
msRTCSIP-PrimaryUserAddress,msRTCSIP-PrimaryHomeServer, msRTCSIP-UserEnabled, msRTCSIP-OptionFlags, msRTCSIP-UserPolicies, msRTCSIP-DeploymentLocator, msRTCSIP-FederationEnabled, msRTCSIP-InternetAccessEnabled.
in Powershell it would be
get-aduser username|set-aduser -clear msRTCSIP-PrimaryUserAddress,msRTCSIP-PrimaryHomeServer,msRTCSIP-UserEnabled,msRTCSIP-OptionFlags,msRTCSIP-UserPolicies, msRTCSIP-DeploymentLocator, msRTCSIP-FederationEnabled, msRTCSIP-InternetAccessEnabled
Hope that helps :-)
Ged