Why do you have to buy a two year contract to activate your iphone?

Answer

You don't.

You can sign up for the monthly GoPhone plan and use the iphone without a contract. Speak to an AT&T customer specialist for more information on how to set this up.

Also, 02UK do a contract per anum, very reasonable price!

Source:iphone-without-contract">http://www.powerglobaldesigns.com/iphone-without-contract

THE REAL ANSWER

Because Apple makes more money