We use Merlin for modifying MS Project files for our clients and then export back to MS Project - when we saw that the iPhone version was available, we jumped on it - frustrating part is that while none of our Merlin projects are password controlled, the iPhone version insists we enter password information. Needless to say the path forward from there is very short. Good start though, but the documentation could be a little more illuminating!
MacIrish about Merlin - Project Management