Please follow only the official mesibo documentation at https://docs.mesibo.com and avoid relying on any outdated or unlinked sources. The page you mentioned is now removed. If it was linked from anywhere in the official docs, please let us know, and we will fix the link.

To customize the call UI, the recommended approach is to use CallProperties:
https://docs.mesibo.com/api/calls/callproperties/

If you have specific requirements that cannot be met using CallProperties, let us know, and we will evaluate whether they can be supported via CallProperties.

Alternatively, if you need complete customization, refer to the sample code here:
https://github.com/mesibo/ui-modules-android/tree/master/MesiboCall

You should also refer to the main call API documentation to understand the various callbacks and APIs used in the sample:
https://docs.mesibo.com/api/calls/