None that I am aware of (that work everytime, and provide 2 way communication). I didn't look much further than SimpleWire because they offered everything we needed - except 27,500 lines of code .. but they just provide the API

It costs the provider money to send the message, so I don't know why people have such an aversion to paying. An unsustainable business model leads to an unsustainable service.
Can't help ya, sorry.