What do you mean by "officially"? Buying is buying. What's "unofficial" buying?I always wondered why people buy phones to put them on a contract with the same carrier, Why buy an AT&T 16gb iPhone 4S for $200 when you can get it for $100 officially?
Typically people avoid subsidies to avoid contracts if that's what you're actually asking about but it's difficult to tell from your poorly worded post.