JavaScript Dynamic Select

<script>
function SelReceiverNameChange(){
  document.frmSendSms.receiverPhoneNum.value=document.frmSendSms.selReceiverName.value;
}
</script>

<form name="frmSendSms" method="post" action="#">

<input name="receiverPhoneNum" id="receiverPhoneNum" type="text" value="" onkeypress="receiverPhoneNumChange()" onkeydown="receiverPhoneNumChange()" onkeyup="receiverPhoneNumChange()">

<select name="selReceiverName" onChange="SelReceiverNameChange()"  >
<OPTION  SELECTED VALUE="">- Choose -
<OPTION VALUE="sym">az
<OPTION VALUE="si">ti
<OPTION VALUE="e">toi
</select>