Since it’s not an actual application, all you need to do to use Wolfram Alpha for iPhone is navigate to wolframalpha.com/iphone in Safari, and if you want easy access to it in the future, add it to your home screen. The company notes in a blog post that a full-fledged iPhone application might be in the cards, and is currently soliciting feedback for it.
The one issue with the current iPhone interface, as noted by Search Engine Land, is that the search results themselves are not particularly well formatted. For example, here’s how a currency conversion displays:
After fiddling around with the results, you can get them in one screen, but they’re still challenging to read:
In any event, Wolfram Alpha seems like a tool that could be useful to have on your phone, moreso if they improve the results interface or better yet, launch an actual application.
More Wolfram Alpha Resources