I personally have an iPhone paired up with my MacBook Pro. So far, I use Nursing Central's online access portal (they have it formatted for iPhone when they detect mobile Safari connecting), and I occasionally use Epocrates online.
Epocrates was one of the first to demonstrate their capabilities with the new 3rd party developer SDK, and made a fully functional Epocrates program in just 2 weeks...so I am SURE we will see the iPhone as a major contender in the health care fields.
A few of the head honchos at our hospital's school of medicine are currently having me educate them on the implications of the June update, to see if they should switch all departments to iPhones.