online mobile phone deal review

Hi, i was very aprehensive when a friend of mine told me he had just receieved a free dell laptop when renewing his original mobile phone contract with t-mobile.
He told me he was thinking of renewing when his contract came to an end this year, He was happy with the service, free minutes and texts he got from t-mobile.
After renewing his contract he asked me if i was interested in a better contract, I told him i was on pay as you go and was happy because i was in controll of how much i spend. He asked me my monthly cost and i told him approx £40-50 believing this was cheap as i had no line rental, He was quick to point out that i could be better off with a contract as i could get free minutes and text, Where's the catch i asked thinking i would have to fork out for a phone.
Anyway i visited the site: www.onlinemobilephones.info who my friend recomended, I have to say i was a little blown away by the offers, How can these companies give away brand new lap tops, 32"tv, sony ps3 and even cash? it must cost them and i just did'nt get it.
I applied for a phone i liked (nokia ) and agreed to a 12 month contract. The cost each month is £29.99 and for that i get 800 mins calls, unlimited text and a free gift, Im actually £10-20 a month better off and i got a free gift, my fried got a bonus for recomending me (not sure how he got this) anyways i got my phone delivered with the free gift and i even got to keep my old number, The switching over of my old number only took 2 days after a quick call to the network provider