I have an iphone 3GS and a few months back I lost the ability to tether from the settings menu, I thought this may have been a bug in the ios4 with jailbreak, but then I just purchased an Iphone 4 and have the same problem on my XT sim, anyone else seen it or been able to get it back to the menu?

I also notice that carrier settings cannot be uploaded to the phone through itunes anymore, is there a way to set the voicemail  number and change the carrier logo, or has all this functionality been removed?