Error is correct then. But the conformance requirement was a bit strange... can you explain what you mean by "MUST be raised on the TelephonyManager"? To get an Error to the TelephonyManager, you will need to call some function on the TelephonyManager. In the last version of the spec you were using an Event - I don't think that is a good solution here. Instead, this sounds like a good place to use a Future.

```JS
Future startTone(DOMString tones, optional ToneParams params);
```

so, then the fail function is called with a new Error:

```
x.starTone("123").then(success, fail);

function fail(error){}
```