Great question, the following is a screen shot of a high end user.
You can simply access your current app usage by going to the apps data and storage usage.
This particular app shows 23,277 messages sent in one year at a total of 151.5 MB divide by 12 months would be 12.63 MB per month. Not much usage for text
The app shows 711.5 MB of media, meaning calls, voice, video and photos. That’s 59.29MB per month.
You can expect a high end user needing less than 100 MB of internet usage for an entire month. Not much for such a highly used app feature.