At Twilio are focused on creating a platform that enables developers to build value-added applications for their customers. To this end, we have never offered a product that allows developers to send out messages without a number to receive replies. We believe two-way messaging offers our developers the ability to create unique application experiences and has real value to our developer community. As such, we choose to be agressive with cheap outbound pricing and charge for incoming messages.
This is our first foray in to SMS outside of North America though so please send me feedback on your thoughts at patrick [at] twilio