take it from someone who has an iPhone 3G and is currently got a contract with Orange, stay away and wait around for Vodafone to release there tariffs and services. Orange haven't the blind foggiest about the iPhone and won't do for quite some time as most of the customer representatives aren't very clued up about the features and use of the latest phones. Also i was getting them to check some stuff out and got them to switch of all internet related features from their end, including GPRS and my iPhone was that sophiscated that it was bypassing all of that and accessing the Orange data services, for which they decided to charge me £1 for a 1mb's worth of data.
Also at these prices might as buy the phone sim free and get a sim only tariff, better value for money.