Click on the following link using an iPhone: Tip Calculator
Then press the " " button to add it as a bookmark.
You can now access this basic Tip Calculator (written by W. Clawpaws) by simply opening the saved bookmark, even with no active data connection.
W.Clawpaws has even posted a one-line Perl script that converts HTML into a data: URL.
There are a few caveats to the code that can be stored in bookmarks, and very large bookmark data files may crash the iPhone, but this is a truly tremendous bit of progress.