Where are you looking? I know both SMS and Whatsapp depends on the member "enabling" those functions for their number in Member Tools. So the button's appearance is on a per-member basis.
I'm not sure what the default is.
Have you searched the
Help Center? Try doing a Google search and adding "site:churchofjesuschrist.org/help" to the search criteria.
So we can better help you, please edit your
Profile to include your general location.