https://developers.google.com/appengine/articles/twilio
Twilio is a service that provides APIs for making and receiving calls from the Web. You can also ask to press the tone, such as "Press the number 1?". Useful for automatic voice guidance and televoting. It is quite cheap with the price setting of how much it costs per time
I will not write about the procedural details of coding in particular. If you know it, the above article is quite good.
I think there was a person who said "What's that" (meaning what kind of cooperation, maybe) when the announcement was made. GAE doesn't work with Twilio at the API level or billing level, right? It's just an introduction to a good use case that says, "If you fetch the API and use it, you can work together smoothly." Actually, the charges are different, and the document says "Read over there".
However, there is a story that it is profitable to start now because you can get a free use frame like a campaign. GAE and Twilio aren't too bad in my opinion (Python, Java, PHP examples are plentiful, PHP examples yes). I'm curious about this area as a GAE heavy user. Unfortunately, there are no Go language examples (and SDKs) as far as I can remember.
In Japan, KDDI has become the contact point for Twilio's localization in Japan in the form of Twilio for KDDI, so Japanese support has improved. It seems that SNS cannot be provided in Japan due to the restrictions of Japanese law, but when it comes to speech, it has the long-awaited Japanese speech synthesis that did not exist in overseas Twilio.
Even though I was a relatively beginner of GAE, I was able to review GAE, review Twilio, and collaborate in one day. For Twilio, the challenge is what to do with your ideas.