Can you buy an iphone without a carrier?

Ok, so the new iPhone 6 is coming out. This would be no big deal to me; but I'm two generations behind with an iPhone 4s. So, when I can get a job I want to get a new phone. Either a 6 or 5s. Let me also say my iphone is locked and apparently can't be unlocked because the account no longer exsists. Anyways, My step mom says she will put me on her plan when i get my phone, but I would have to pay $22 a month to her for adding me on ( i know, she's a wicked step mom, heh). I won't be able to do that right away. So is it possible to buy a phone at Apple without a carrier like at&t or t-mobile? Basically, it would be a big iPod. I just want to be able to activate it when I can but already have the phone so I'm not having to save up more money to pay for it and everything else.

Usually when you add a plan to an existing account the phone comes out really cheap. I believe the iphone 5s is around $99 and the iphone 6 is around $200 with a 2yr contract. So why not just wait till you have a job and save up either 100 or 200 bucks, and then have your mom add you to her plan. It would be alot better than spending $550 dollars on a iphone 5s or $649 for the iphone 6.