function getHTTPObject()
{
	if (window.ActiveXObject) return new ActiveXObject("Microsoft.XMLHTTP");
	else if (window.XMLHttpRequest) return new XMLHttpRequest();  
	else
	{
		return null;
	}
} 

function setOutput()
{
	if (httpObject.readyState == 4)
	{
		var r = httpObject.responseText;
			
		document.getElementById('callbackcontents').innerHTML = r;
	}
}

function doWork(f)
{

	httpObject = getHTTPObject();
	if (httpObject != null)
	{
		httpObject.open("GET", "ringback.htm?" + f);
		httpObject.send(null);
		httpObject.onreadystatechange = setOutput;
	}
}