£79.99 on O2, Vodafone and Virgin pay as you go upgrade. However all CPW pay as you go phones are unlocked.
Only in white, orange or Matt black, this is a cracking deal for a sim free, 4G hd screen phone.
Also come with Office 365 for free for 12 months. This is worth £59 on its own.
Possibly another £5 off via Quidco for pay as you go purchase. NB I got nowhere with the linked HDUK £30 off code!
Direct link: http://www.carphonewarehouse.com/phones/microsoft-lumia-640/handset?colourCode=BLACK
Topcashback pay £5.25 for a PAYG phone.