I'm with Three and when I got my iPhone they gave me a Bumper - I can't remember the brand but it wasn't Apple and I wasn't overly impressed with it - either way it done me for a couple of days until I got a decent case.
Also for those that doubt the unlimited internet and tethering, check this out:
And finally, for the moment of truth! Is the One Plan on Three really unlimited? Well here is my April 2011 bill showing I used around 325GB of data in March 2011