I have a customer that is using a 3rd party voicemail solution and as such cannot use the voicemail feature of the Jabber client.
Is there a way to make the voicemail section from the client not show up? with it not configured the voicemail section has a big red ! and an error that it cannot connect specfied server, eventhough there is none.
The below answer is under the assumption that you are using Cisco Jabber for Windows ON Prem deployment.
You can goto CUPS Admin Page ->Application -> Cisco Jabber -> Voice Mail Profile and make sure nothing is configured there.
Also if you have Cisco Jabber for Windows deployed for On Prem, please provide the content of the jabber-config.xml