title: Regex for Mobile Number with or without Country Code
body: <p>I need to validate a text field in my registration form for which I want a Regex. </p>
  
  <p>The textbox will accept a mobile number like 9999999999(10 digit - starting with 7 or 8 or 9).
  The user may alternatively write +919999999999, where +91 is country code (+91 for India, but can accept any other like +110 or +52), or he may also write 09999999999 (first 0 for own country)</p>
  
  <p>Here, the user have 3 choices, </p>
  
  <ol>
  <li>adding the mobile number with country code </li>
  <li>simply without country code or 0 prefixed</li>
  <li>With a zero prefixed in mobile number.</li>
  </ol>
  
  <p>Though not required, my page is in asp.net, and I am using built-in regular expression validator.</p>