I've used the Brodit ProClip phone mounts before, and have been very pleased. (
www.proclipusa.com) Its a 2 part system You buy a bracket that is custom designed to clip on your dash, and then a second part that is custom designed for your phone. There are 2 mounting locations available for an 04 Prius:
Then combine it with an iPhone mount (several types available, but I like this one):
