What does the 18 month financing mean for an iPhone at best buy?

I just got a job and I really want an iPhone… And I need to know everything about contracts and stuff for that.

It means instead of paying the whole amount up front, you pay the amount (plus interest if applicable) in 18 installments. Don't forget you also have to have a phone plan as well. There are very high penalties for early cancellation and so you need to also insure your phone. I'd also get an extended apple warranty. If you have no insurance and no warranty, if you lose or break your phone, you'll still be paying your 18 months of installments regardless!