With a little bit of work it may be possible to purchase an iPhone 6 16GB at Curry's/PC World for only £400. Follow the below instructions for a massive £150 of RRP.
1) Go to GiftCloud (https://www.giftcloud.com/uk/choose/gift/value) and buy 5 separate Curry's gift cards for £100 with the current 20% of promotion that becomes £80 each = £400 for £500 (it has been confirmed that these can be stacked as they are treated as cash)
2) Use the o2 Priority moment app to get a £50 off £500 spend code to use at Curry's/PC World. (Although this states it cannot be used on iPhones, it has been confirmed as still working for most on a earlier thread)
3) Go to your local Curry's/PC World which stocks iPhones (N.B. not carphone warehouse) and use the o2 priority code and your vouchers to save £150.
Save a possible £15 more, by going through topcashbach. 1% on online purchases at Curry's and 3.15% on voucher purchases at Giftcloud.
Credit to goonertillidie for posting about the vouchers originally.
These have also been confirmed as unlocked from Curry's on a previous thread.