This is my first post but hopefully it will help some of you looking for a cheap phone contract. BuyMobilePhones.net have a selection of T-Mobile contracts which offer 18 months free line rental on an 18 month contract. Possibly the same for 24 months, but I haven't checked. So far as I can tell, it is on all of the bundles up to £30/mth and they all include a free swappable bundle, so you can have unlimited texts, unlimited (1GB) data, unlimited landline calls etc. I received 600 mins, 500 texts and unlimited data on a £30/mth tariff.
From the link, click "phones" under the tariff you are after, and then choose which handset you want. Only the ones with the highest auto cashbacks appear to offer 18mths free line rental if you click on "free deals" under the handset. The phones themselves aren't exactly great but this would be a great deal if you don't care about the internet, or already have a phone to use the sim with. And you can always recycle the phone in that case to get even more money back (the Nokia 2680 seems to be the best for recycling at around £15).
I know some people don't like redemption schemes, but I have had four contracts like this previously and so long as you set a reminder in your phone calendar to send the bills off recorded delivery, you should be absolutely fine. TopCashBack also have £25 cashback for this website.
Hope this helps some people. Oh and I phoned their customer services who have a landline friendly 5p a min number, or a number that is free on mobile inc. minutes, and my call was answered literally within 20secs which makes a very pleasant change.