We currently require users to enter a mobile phone number that is used for receiving notifications as text messages.
We've had multiple cases of people mistakenly entering their landline number instead, which is why we implemented a rather strict check for cellphone numbers (the country is France, in which all cellphone numbers start with known prefixes).
However, validating on a specific prefix feels wrong to me on some level, especially since some countries have no known cellphone number prefix.
- I've also thought about displaying a warning text (e.g. "your phone number seems invalid, please double-check that it belongs to a mobile phone") without preventing the user from saving the form.
- I've thought about validating those numbers (e.g. with a code sent to the user), but the effort seems disproportionate for us.
Is there a good way to handle that besides what I have listed?