I guess I was a little confused about what this actually does. This does not do any calling, right? It just issues a command to Plivo to call Mom's number and then, when she answers, call a second number (assuming this to be the house where this device is located). At that point the RasPi is totally out of picture as the conversation happens phone-to-phone (possibly getting Plivo out of the picture too?). So you've created an external one-touch speed dial. Is that accurate?

Side note: Is there something that prevents me from building this and putting in two numbers I am not associated with? Push button. Two random strangers get calls from each other. Hilarity ensues. That type of thing is kind of scary.