There are a number of different ways that you can purchase a new cellphone.
You can either pay for a new device through monthly installments or buy the phone at the retail price (outright).
Outright purchase applies means that you are buying the phone at the standard retail price - for example, directly from the Apple store
If you purchase an iPhone 6s, it will cost you around $650 upfront as the outright cost. If you were to pay for the iPhone 6s through monthly installments, it will provide a payment plan for 24 months instead of paying outright.
When you pay for the device outright, you will own that device immediately, its yours. If you were to pay through monthly installments you would own the device after you complete your payment plan.
Outright purchase will be more expensive as you are paying everything in one go. It all depends on whether you want a basic phone, a mid range smartphone or a top spec phone like an iPhone or Samsung
I have provided a list of devices below for you to see some outright costs currently on the market. In the first link, I have provided outright options for an iPhone 6s. In the second link, I have provided outright options for a less expensive model iPhone 5s and in the last link, I have provided outright options for a Samsung Galaxy s5
Use these links to give you a general idea of what outright purchases are