All models of Apple's iPhone 3GS may well be out of stock almost everywhere in the UK but we've managed to find some available most of them as pay as you go models complete with warranty.
That said, proceed at your own risk. Buying such an iPhone also means that you won't be get free unlimited internet and WiFi for 12 months, nor will you be able to get your iPhone 3GS replaced quickly.
Your best bet is possibly to wait for the iPhone to come back in stock. The 16GB model from O2 is on sale for £440.40 while the 32GB version costs (opens in new tab) £538.30
The first obvious place to get a legit iPhone 3GS is on Ebay where there are hundreds of them already on sale. We chose Buy It Now auctions where you can literally click and purchase your items within minutes.
Hidevolution (opens in new tab), a US-based 100% positive Ebay Power Seller with nearly 700 positive feedback, is selling an iPhone 3GS (16GB Black) version for $725 including delivery.
Closer to home is an unlocked Apple iPhone 3GS Black (opens in new tab) model on sale for £589 from 123_sahar2008 who is based in Blackburn. Ebay protects purchases made by Paypal but it won't be able to act if additional charges like value added taxes are imposed.
If you would rather pay and collect your iPhone 3GS, then expect to pay around £550 for the 32GB iPhone 3GS and £450 for the 16GB model from Buy-and-Sell Specialists (opens in new tab) Computer Exchange.
All the items sold there come with one year warranty. The products are complete with box and sold as new and can either be collected instore (they've got dozens scattered across the country) or delivered to your front door.