☝No Voicemail feature lookahead possible: Currently, there is no way to check ahead if a transfer target (MS Teams User) has Voicemail features enabled. This is a design limitation by Microsoft which Nimbus currently cannot circumvent. 

☝Voicemail feature IT policies: Additionally, the Voicemail feature may also be deactivated as part of a tenant-wide IT policy by your administrator. There are also known cases where Microsoft accepts transfers to Voicemail but the recipient has no means to check (e.g. due to MS Teams Client / License restrictions). 
→ We highly recommend using “Transfer to voicemail” related Nimbus features only in case Voicemail is generally enabled for the Microsoft Teams user.

☝Unsupported Scenario - PSTN call forward to Voicemail within own Tenant: When inviting an internal user via PSTN (e.g. in a Attendant - Consultation Call scenario) with Voicemail forwarding enabled:
⮑ The call will be redirected, but the receiving user will not hear anything.
⮑ In Nimbus the call will fail.

🔎Analysis: This scenario is unsupported because MS Teams will auto-resolve the PSTN Number and generate a federated call. The Nimbus bot will run into a timeout and the receiving user will only get an empty Voicemail.