function validatecallback()
 {
  var cbname, cbemail, cbnumber, cbmessage;
   
   cbname    = window.document.forms['msgform'].cbname;
   cbemail   = window.document.forms['msgform'].cbemail;
   cbnumber = window.document.forms['msgform'].cbno;
   cbmessage = window.document.forms['msgform'].cbmessage;
   if(trim(cbname.value) == '')
   {
      alert('Please enter your name');
      cbname.focus();
      return false;
   }
   else if(trim(cbemail.value) == '')
   {
      alert('Please enter your email');
      cbemail.focus();
      return false;
   }
   else if(trim(cbnumber.value) == '')
   {
      alert('Please enter your phone number');
      cbno.focus();
      return false;
   }
   else if(!isEmail(trim(cbemail.value)))
   {
      alert('Email address is not valid');
      cbemail.focus();
      return false;
   }
   else if(trim(cbmessage.value) == '')
   {
      alert('Please enter your message');
      cbmessage.focus();
      return false;
   }
   else
   {
      cbname.value    = trim(cbname.value);
      cbemail.value   = trim(cbemail.value);
      cbnumber.value = trim(cbno.value);
      cmessage.value = trim(cbmessage.value);
      return true;
   }
   function trim(str)
	{
	   return str.replace(/^\s+|\s+$/g,'');
	}
   function isEmail(str)
	{
	    var regex = /^[-_.a-z0-9]+@(([-_a-z0-9]+\.)+(ad|ae|aero|af|ag|ai|al|am|an|ao|aq|ar|arpa|as|at|au|aw|az|ba|bb|bd|be|bf|bg|bh|bi|biz|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|com|coop|cr|cs|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|edu|ee|eg|eh|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gh|gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|in|info|int|io|iq|ir|is|it|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|mg|mh|mil|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|museum|mv|mw|mx|my|mz|na|name|nc|ne|net|nf|ng|ni|nl|no|np|nr|nt|nu|nz|om|org|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|pro|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)|(([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5])\.){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5]))$/i;
		
		return regex.test(str);
	}
 }