As Mandyloo said instead of searching for an used iPhone from a layby store, You can get some best deals on iPhone models from Ebay.Com Network locked iPhone models would be very low in cost. Some people would sell temporarily unlocked phones for more cost. After purchasing it, Somehow you need to spend again to unlock it when the device gets re locked on future updates. Instead you can get a network locked iPhone and unlock it yourself permanently. One of the safest and easiest way to unlock an iPhone permanently is the remote unlocking service. You can get the remote unlocking service for an iPhone from http://www.theunlockspot.com/apple/rs16wp8/ at affordable cost with easy unlocking guide. This method of unlocking doesn't require a jailbreak too.
You cant put an iphone on layaway. Your better off saving up the money, or buying a used one off ebay or craigslist. Cellphone service providers dont offer a layaway plan.
aww stankkk!!!! but thanks for answering :D