Sprint has signed a deal with Apple to buy over $20 billion worth of iPhones over the next 4 years, reports the Wall Street Journal. And it's a move that suggests that the operator could even go completely iPhone-only to meet demand.

The deal, which comes just hours before Apple is expected to announce the latest iPhone at its "Let’s Talk iPhone" event in Cupertino, sees sprint promising to buy some 30.5 – 32 million iPhones between now and 2014.

If true, Sprint would have to sell almost 8 million iPhones a year.

While many experts believe that could be possible, with Verizon having sold 12 million already this year (since February), it means the operator would most likely have to scale back its support of Android and Windows Phone 7 devices to ensure it pushes those kind of numbers.

"The number 3 wireless company is making a multibillion dollar gamble that Apple's gadget will be the ticket to a turnaround, even though Sprint chief executive Dan Hesse told the board in August that Sprint would likely lose money on the deal until 2014, according to people familiar with the matter," reports the US paper.

Sprint currently doesn’t stock the iPhone.

According to the WSJ, the US operator is fed up with losing customers to iPhone carriers AT&T and Verizon.

The lack of the iPhone is "the number 1 reason customers leave or switch", Hesse said at an industry conference last month.

And the Sprint CEO is hoping that by stocking it he can save the company which has struggled of late in a competitive US market. Its stock has lost more than 80 per cent of its value since the iPhone hit the market in June 2007.

Verizon added the iPhone 4 to its shelves in February after 4 years of waiting and immediately saw strong sales even though rumours promised an update.

Apple’s "Let’s Talk iPhone" event kicks off tonight with the expected launch of a new iPhone or two.

In related news, BGR.com is claiming the Sprint will get an exclusive model because of the deal cited by the Wall Street Journal, but provides no concrete evidence. The site's track record has been hit and miss in the past when it comes to Apple rumours.

Could Apple have just “bought” itself an operator in the US? Let us know what you think in the comments below...