I want to track adwords conversions when a user clicks on a phone number on my page coming from a google search. That's what i did:

I added a piece of script based on detectmobilebrowser.js to check if the user is using a mobile. you can see my script [here](http://www.servimulti.com/detectmobilebrowser.js) 

I have a link on a phone number like this:

```
<a onclick='clickNumber()' href="tel:9xxxxxxxx">xxx xxx xxx</a>

```

And this is the javascript triggered when someone clicks on the number (notice that the conversion is only tracked if the click comes from a mobile browser):

```
<script type="text/javascript"> 
function trackConv(google_conversion_id,google_conversion_label) {
         var image = new Image(1,1); 
         image.src = "http://www.googleadservices.com/pagead/conversion/"+google_conversion_id+"/?label="+google_conversion_label+"&script=0";      }
function clickNumber() {
    if(isMobile) {
        trackConv(xxxxxxxxxx,"xxxxxxxxxxxxxxxxxxx");
        }
}
</script>

```

The conversion is tracked when someone clicks on the phone number, but then they have to accept to call that number. How can I know when someone is actually making the phone call. Is ther any kind of API or event for such thing?