And a lot of the people that break them have insurance or just won't bother, so it might not be as lucrative a plan as you might think.Alot of people have iphones and a lot of people break them so it would seem logical to be able to fix them.
You also need to take practical considerations into account. Will you offer some guarantee over the repair? If I send my broken iphone off and have it repaired for £50, I'm going to want some form of guarantee it won't break the next day. If it does and you can't re-repair it, what are you going to do? The traditional "big company" approach would be to pass on a new iphone and swallow the comparatively small loss. As a small company, I doubt this is something you can really do...