What's the catch with these mobile phone offers?

Does anyone know what the catch is with these crazy offers you see on telly all the time?

A free laptop and PS3, a free moped...sounds too good to be true?

Example: www.dsf-mobil.de

One or sometimes even two 24-month mobile contracts, with a rather high base fee or minimum charge, the rates per minute are also rather high, and they won't sponsor you a new mobile after 24 month if they didn't make any profits with you.

It's a frighteningly expensive phone contract. €0.39/minute to landlines and your own network and €0.79 to other networks, minimum €14.95/month, minimum 24 months. Compare that with a lowly pre-paid contract with no monthly minimum, less than €0.09/min to all networks and no commitment and you see where they make their money can afford to give you expensive gifts

Yeah and the bottom line you will pay more than buying your own laptop or PS3 than signing up with those offers.