[dimitry]

This is an API, not an application. In other words, if you want the end-user to get an SMS reply, you have to write code and instruct the API to send a message.

Mobivity gives you simple marketing tools (voting, pre-defined messages to reply with, etc.).

[petesalty]

Actually, no, Mobivity give you an API to send and receive SMS messages, and they do it in pretty much the same way this site does. I know this because I've used them to do exactly that. I know it does the the marketing as well but it has a fully fledged SMS api too.