Is it possible to read these forums on an iPhone ?

Possible yes. Use you phone as a normal browser. Not a very nice experience though as the formatting is awful on the small screen. Spend forever scrolling around the page, zooming in and out and accidentally "clicking" on things you didn't mean to.

http://community.betfair.com/go/forum/popupExtra?output_method=iframe

Thanks. Of course. These are just web pages so I can view the forums through the browser, as you said, via the link above.

Posted from my iPhone!