Mobile number validation using regex CRM 2011

function validateMobile(context){

var mobi =context.getEventSource().getValue();

mobiRegex = /^(083|084|085|086|087|088|089)\s?\d{3}\s?\d{4,5}$/;

if(!mobi.match(mobiRegex)){

   event.returnValue = false;

   alert("The format of the mobile no is incorrect") ;

   }

}