Welcome to the forum.
You cant buy an iPhone from them without a plan from AT&T because in order to buy it, you have to activate it in the store. If you buy the phone and plan on canceling your service within 30 days of service with them, you are forced to return the phone.
Yes, your best bet is to get it through eBay. You can also check places like craigslist and things like that.
Also, you wont be able to buy it new because they are not being made anymore.
Hope I answered your questions
