Disclaimer: I neither own, nor endorse, the iPhone platform. I have seen several of the HP clones for the iPhone, and wish I had one. ;-)
I do own the MathU RPN calculator (modeled after an HP-like calc) for the Palm Treo. They just sent me an email saying that their port of the MathU calc for the iPhone is available for a limited time for $0.99 from the iTunes store.
So all you iPhone geeks, go give it a try and let us know what you think! ;-)
thanks,
bruce