function checkform(form){
  var emailreg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
  var phonereg = /^([0-9_\-\(\)\.]{7,12})$/;
  var name = form.contact_name.value;
  var email = form.contact_email.value;
  var phone = form.contact_phone.value;
  var comment = form.contact_comment.value;
  
  if(name == '' || phone == '' || email == '' || comment == ''){
    alert('All Fields are Required.');
    return false;
  }else if(phonereg.test(phone) == false) {
    alert('Please check your phone number.');
    return false;
  }else if(email != 'N/A' && emailreg.test(email) == false) {
    alert('Please check your email.');
    return false;
  }else{
    alert('Your details have been sent. Thank you!');
    return true;
  }
}