The Exact Editions system now makes ISBNs clickable and the first examples (for subscribers only, as the issue is behind the subs pay-wall) are in the current issue of Opera magazine.
This is the example that I tried first:
Which today takes you to this page. ISBNs have recently gone to 13 digits (that allows for a lot of books and publishers) but Amazon is currently using a look-up table for the 13 digit numbers, which is why you land on a results page. Currently we target the Amazon UK pages by default, but this should become a configurable option.
Clickable phone numbers and clickable ISBNs......more good things for the iPhone.