may be you should try this :
var myJSONtext = '{"call": "9880039959","sms": "hello","url": "www.google.com"}' ;
CallParameter.myObject = eval('(' + myJSONtext + ')');
function CallParameter(value) {
if (value!="")
{
alert(CallParameter.myObject[value]);
}
}
CallParameter("call") ;
CallParameter("sms") ;
CallParameter("url") ;