To get at this price use the 15% off voucher code (XX922 or XX587) which will take £26.85 off, leaving £156.10. 8% quidco (£12.17) takes it down to £143.93 which is an impressive price for this phone on o2 network.
£143.93 including delivery.
o2 network phones normally have their phones unlocked (open to any network) but i cant say for definate until i get mine through the post tmrw.
edit: sorry dont think this will be unlocked as it is PAYG and only o2 contract phones are unlocked as grabbit has pointed out.
Mobile Phone Specs: http://www.nokia.co.uk/find-products/all-phones/nokia-6700-classic/specifications