1) It sent me a text letting me know the message had been received, and another with the result. The confirmation was nice, but since the messages came 2 seconds apart you could skip the first one and save 3 cents.
I created a similar app, but primarily for India (using India local number). But it should work internationally also if you are willing to pay international SMS charges (don't know at what premium). I've hosted at appengine first to see the response http://sms2ping.appspot.com Do let me know if someone tries it. BTW I get a response message free so am not paying to send out messages as response
The problem is Twilio provides no way of billing end users.
In this case it comes down to a micropayments problem (which still haven't been solved sufficiently). So you either have to charge up-front for a monthly service fee of a reasonable sum, or stick adverts everywhere which will hopefully cover your costs.
It's a major flaw for the platform if you want to build a business off of it (I've been playing around with a per-monthly-fee service concept recently).
http://blog.twilio.com/2010/02/resources-for-getting-started...
-danielle @ Twilio