A python wrapper for the Google Voice API. Potentially allows the sending of SMS messages (or receipt of SMS messages) via Google Voice for free in the US and at GV costs overseas.
Similar to Twilio, send / receive voice & sms via APIs. Doesn't appear to be as quickly evolving as twilio, but free for development use.
Developer APIs for placing calls and sending SMS messages. Handles both incoming and outgoing, but only sends texts in the US and only has incoming US / Canadian numbers.