Some handsets appear to switch to Edge even when 3G is available.

According to the Wall Street Journal, they have claimed that Apple is set to release a fix within weeks.

Further details available here: http://www.reghardware.co.uk/2008/08/15/iphone3g_patch/.

I missed this earlier in the week, but Business Week have also got an article regarding the Communications chip that is used by the iphone. They suggest that the chip contains faulty software, but this should be able to be corrected by a suitable update. Read more here: http://www.businessweek.com/technology/content/aug2008/tc20080813_430402.htm

And more here: http://www.appleinsider.com/articles/08/08/14/iphone_3g_reception_issues_to_be_relieved_by_software_update_report.html