Collecting mobile number

Hello Dribbblers! Need your feedback.

User can Register or Log in without mobile number, but for certain services or communication purpose collecting mobile number is mandatory.

While using the app, we will ask user to provide their mobile number, where user can ignore this popup or alert and continue using the app.

From given three options A, B & C, which would be the better experience.

Please do share your comments.
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Would love to hear your feedback 😊