If you are developing mobile application that needs phone verification – Twilio is a good start point. They also have a promotion for Google Cloud Platform

Here is an article how to integrate Twilio to your Google AppEngine project Upd: seems this code doesn’t work anymore

I’ve recently tried to integrate the latest Twilio python library to my GAE application. Version 3.6.2 fails with NotSupportedOnThisPlatform – Google Cloud Platform doesn’t support certificates in httplib2. Use 3.5.2 version instead.