Found this out yesterday when was getting a 12 month sim only contract online which gives you 300 Mins and Unlimited Texts. As i was going to checkout started chatting to customer services and he gave me a promotion code for a FREE Samsung J700i. Plus then your also getting £50 Quidco or Topcashback (On £10 a month contract) which was making it a even better deal.
Select the 12 Month Plan you would like.
On the checkout enter promotion code: samsungfree
Plus go threw Quidco or Topcashback for upto £150 cashback.