Onavo, as we just reported, is a magical iPhone app which literally shrinks the data your phone uses and thus your roaming data bill when you are travelling. It launches today and I caught up with CEO and co-founder Guy Rosen at The Next Web conference in Amsterdam.

I’ve actually been using Onavo for weeks, since a trip to Tel Aviv and a random meeting with Rosen. Although the compression happens on Onavo’s servers, it’s changed nothing about my iPhone use – other than the fact that it’s saving a noticeable amount on roaming costs when I am travelling in Europe. It may even be between 20-30%.

That of course is highly disruptive, and will be of great interest to both users and carriers.

While free, Onavo plans to do some interesting things with its service. They are not yet revealing these but I think we can speculate that evenutally there may be some premium aspect to this. But whatever happens I think I’d rather pay Onavo a small amount than a LOT to my carrier. This is quite simply a “must download” app for iPhone users. Here’s an iTunes link.

Here’s the interview: