If you agree to sign up for 12 month rolling/renewable contract Free Evening and Weekend Call Package, or a £4.95 24/7 call package. BT will offer you a free HP printer worth £57 whilst stocks last.
The offer only appears when you start to fill in online application. I understand its a HP Deskjet D4260.
Note: At the end of each 12 month minimum period the contract will be automatically renewed for a further 12 month minimum period unless you tell them otherwise. They say they will write to remind you when your contract is nearing the end of a renewable period.
http://www.productsandservices.bt.com/consumerProducts/displayCategory.do?categoryId=CON-TOG-OPT-R1&s_cid=con_FURL_calls_choices