• Jailbreak the phone (see iphone-dev.org)
• Install a package manager like Cydia (perhaps jailbreaking will give you that for free)
• Install openssh package on your phone. Turn on the wireless.
• Use an sftp client to copy /System/Library/Carrier Bundles/Bharathi_XXX.bundle/carrier.plst (ssh root@your_phone’s_ip) to your computer
• Use this link to convert the plst file to a text file: http://140.124.181.188/~khchung/cgi-bin/plutil.cgi
• Edit the file and add the following text (above carrier name): AllowEDGEEditing
  
• Place the modified file in the same directory back on the iPhone

After the above steps (you may have to shutdown and restart the phone) you will see a “Cellular data network/EDGE” under Settings->general->network