If they install the Coda app and allow notifications, the Coda notify feature should work this way.
If you have the app on your phone, open it, log in, then click on the 
icon at the bottom right to open notifications, then click the 
icon at the top right and you can turn notifications on or off for both email and mobile.
Personally, I use the browser shortcut that goes directly to the doc I want, then just install the app to get the notifications.