Here is a simple one line change which will make your webpages viewable well on iPhone and Blackberry. Add the following to your HTML HEAD section:

Apple is using the following on their RSS reader website:

The other parameters you can experiment with: initial-scale (first loaded scale), user-scalable (boolean), minimum-scale (default 0.25), maximum-scale (default 1.6).

There is an active discussion on this topic here.

Viewport is part of CSS 2.1 (link) specification. Viewport is a window or through which users view a document. User agents may change the document's layout when the viewport is resized.

Update: I have added the solution to this site's template. All the pages should now be readable on iPhone & Blackberry. If you own an iPhone I would appreciate if you can view this site in iPhone and let me know how it looks.