What speech recognition service does the Web Speech API use?

I noticed in the documentation, that there is a serviceURI attribute. Documentation

The serviceURI attribute specifies the location of the speech recognition service that the web application wishes to use.If this attribute is unset at the time of the start method call, then the user agent must use the user agent default speech service.

So what is the default speech service in PC Chrome, Firefox or under Android/iOS? How can you change or get the currently used serviceURI?