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I would try the following:

Admin Portal > Users > Roles > Create a new role

as a starting point select whatever role your sales users currently have (for example Standard(International))

Next you need to select permissions.
From POLICIES remove Voicemail.
From USER SETTINGS remove Voicemail settings.

After you create this new role, you need to apply it to your users. You can use a template to apply it to all sales users simultaneously.


I am not sure if this would remove the voicemail button, it might remove it. But even if the Send to voicemail button remains it would send callers to an Announcement and disconnect, i.e. your users won't be able to abuse it.