Drupal 7: SMS notification for all users (anonymous + registered)

Hi everyone. I have a Questions and Answers site running drupal 7.56. I would like to send users (anonymous or registered) SMS notifications when questions are answered or updated.

My questions are:

1. how can I capture the mobile phone number for anonymous users

2. how to send SMS notifications on updates or new answer for to users

Thank you for the input.

Source: https://www.drupal.org/taxonomy/term/22/feed