What would the monthly bill look like while owning a Samsung Galaxy S5?

I am attempting to figure out if buying a smartphone would be a good investment. I have a very minimal income, but also no phone and it s not impossible to get around without one, but it makes it difficult to communicate with others, obviously.

Could anyone give me a good estimate of what the cost would be, both in buying the phone and what I would be paying monthly? I know it depends on what service provider you have, but I need a very simplistic, general overview of what to expect.

Thanks!
Added (1). Or what would it cost to own a smartphone, any brand, in general? Thanks!

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