A whole heap of voice and sms APIs, in a similar vein to twilio / tropo, but seemingly a broader offering, and possibly a later entrant to the market.
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.
Interesting text to speech web service. Prices start at $75/mth plus 0.1c / minute then step up to $200/mth plus 0.01c/minute.