Edited by author 08-02-2006 08:19 AM
It is definitely possible to read barcodes with a cellphone without changing the optics; I have done it. See http://sourceforge.net/projects/readbarc/. ReadBarC is an open source UPC barcode reader which will run on Symbian OS V6.0 cell phones. Using a Nokia 6260 and this application I can read UPC barcodes of the sort (and size) you see on cereal boxes.
The trick to dealing with the focus issue is to predict what the barcode will look like out of focus, and to compare that with the image captured. I explain how this is done on that page.
Below is a screen capture from the application, showing it reading a barcode from a magazine.