Build a Free SMS Robot with Google Voice

I have been look for a free SMS API since April, when my previous free SMS provider, IMified, announced its shutdown.

Zeep Mobile claims to be free forever (because it is ad-supported), but my sign-up is unanswered after a few weeks. Twilio and Tropo both give developers some free credit, but they charge money for production use. Other resources are suggesting an in-house solution: buy a SIM card with cheap / unlimited text plan, plug it into a old phone, and connect to the server; this still costs money, and is impossible for those using a VPS.

As a Google Voice user, I'm thinking: can I use Google Voice to build a free SMS robot?

Google Voice API

Google, the company who release an API for almost every product, does not provide a Google Voice API.