Does data access work normally from the iPhone?
If so then I think that this should work.
Is this thread of any use?
http://community.48months.ie/t5/Need-Help/Internet-tethering-iPhone/td-p/442
Note that the terms & conditions may not allow for this sort of use but in practice it seems to be OK as long as you don't breach the fair usage limits (e.g. Don 5GB).
