- Just go to http://help.benm.at/ on your iPhone (!).
- Choose "mobileconfigs"
- Choose your country
- Install the mobileconfig file
- Done
With the leaked beta of iTunes 8.2 (prerelease bèta 4) you could upload IPCC files to update your carrier settings. This method was very successful for the enabling of tethering on the iPhone for your carrier.
iTunes 8.2 final broke this ability to upload these IPCC files, unless you execute this line of code in the terminal: (make sure iTunes is not running)
defaults write com.apple.iTunes carrier-testing -bool TRUE
To upload IPCC files, hold alt while clicking on "Check for Update" on the summary tab in iTunes.