Further to my update yesterday, I have now managed to get the Google Wireless Transcoder to be correctly identified and the site now renders the correct mobile content to the browser.
Following up on the instructions based at Webmaster Help I inserted the following into my page.tpl.php file.
Note that you should not need to do this for pages that are served in a mobile friendly content type format *: text/vnd.wap.wml or application/vnd.wap.xhtml+xml. These formats should by default be left alone by the transcoder.
* The device detection script that I use finds best suited content-type and renders my mobi in text/html if the browser cannot handle application/vnd.wap.xhtml+xml. Therefore it serves text/html to Google and I need to insert the afore mentioned HTML into the head of my documents.
Pages for imode for example Google will try to transcode the pages as content type should be text/html.