O2 in the UK have announced that they are accepting pre-orders for the iPhone 3G. Pre-orders will be delivered on July 11th. Existing customers will be able to activate their new phone via iTunes at home .
According to comments on the web it sounds as if the O2 website is swamped and struggling to cope with demand.
Edit – The O2 website is now showing the iPhone 3G as out of stock for online orders and to check back on July 10th for more information. At this time Carphone Warehouse are still taking online orders.