Good idea ( I use Chrome to Phone on my android, to do that kind of think). FYI : I tried the website and entered a random number I got a blank webpage with an error:

Traceback (most recent call last): File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/_webapp25.py", line 703, in __call__ handler.post(groups) File "/base/data/home/apps/s~trnsfrapp/1.354335415123281066/main.py", line 388, in post body=body) File "/base/data/home/apps/s~trnsfrapp/1.354335415123281066/twilio/rest/resources.py", line 1018, in create return self.create_instance(params) File "/base/data/home/apps/s~trnsfrapp/1.354335415123281066/twilio/rest/resources.py", line 295, in create_instance resp, instance = self.request("POST", self.uri, data=body) File "/base/data/home/apps/s~trnsfrapp/1.354335415123281066/twilio/rest/resources.py", line 195, in request resp = make_twilio_request(method, uri, auth=self.auth, *kwargs) File "/base/data/home/apps/s~trnsfrapp/1.354335415123281066/twilio/rest/resources.py", line 168, in make_twilio_request raise TwilioRestException(resp.status_code, resp.url, message) TwilioRestException: HTTP ERROR 400: 21401: +15555557777 is not a valid phone number https://api.twilio.com/2010-04-01/Accounts/AC36119600c07b44d...

Good continuation