It is to enable the landline phone to send and receive texts.
Try the info in this topic from last week (message #5 ref the footnote in the VM phone user guide) to see if the feature is available to you.
There has been a bit of VM 'confusion' in some past topics.
Thank you for this. I am in the red zone that can send and receive texts but my problem is that the user guide for my home phone says to contact my provider for service centre numbers these need to be entered on the handset to be able to send and receive texts. In this situation I am unable to text register to 0000 and need the service centre numbers