People have always been financing cell phones. It just wasn't called financing.
When you paid $200 for a $700 iPhone and signed a contract, you were financing it by paying an inflated monthly price for service - you didn't think the carrier just ate the $500 difference, did you? The difference is, with the old model, the cost of the phone and service wasn't broken out on your bill, and worse, when you fulfilled the contract, your bill didn't go down.
With the new mobile share plans, monthly service is generally cheaper if you pay for your phone outright, bring your own, or are off contract. Finance the phone through Next and your bill will be more similar to what it was in the age of contracts. Next is just more transparent.
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A week after purchasing my iPhone 6 with Next I was in Europe with it, and I have 2 more trips planned in the next few months. It's not that I couldn't afford to buy outright, I could if it was the only option. But it's an interest free loan, why not use it?
But by all means, go ahead with your generalizations that everyone who uses Next must be poor.