Support sending SMS messages

I'm not sure why the test on line 25 of SendSMSTest fails (in the log I see "expected (SMS nuntius), got (SMS nuntius)"), but I think we can deal with it in a followup
I can't use this.onsuccess.bind(this) because this.onsuccess is undefined at this point. I've changed setTimeout(..., 0) to setZeroTimeout.