Apple's latest iPhone OS, version 3.1, may bring along with it Genius recommendations for applications and ringtone downloads, but it also takes away tethering functionality with non-Apple-partner carriers. While that may not come as a great surprise, given Apple's dislike of jailbroken and unofficially unlocked iPhones, the new firmware also blocks tethering for those using "official" unlocked handsets.
Most frustratingly, there is no apparent way to downgrade from iPhone OS 3.1 to the previous, OS 3.0 version. That means that users who bought their officially-unlocked iPhone - for a very high price, needless to say - to use on their preferred carrier rather than, say, AT&T, are now unable to access tethering. As for Apple customer support, they've apparently told affected customers that there's nothing they can do to help.