If you want an iPhone but don’t want to sign up for a two-year contract, you’ve been out of luck. But the popular device is about to cross over into the world of pre-paid wireless plans when it makes its debut on the Leap Wireless network on June 22.

The Leap plan is $55/month and includes unlimited voice and data calls and what the company labels as “unlimited” data, but which is actually throttled after 2.3GB/month.

The catch is that you need to pay for your iPhone than you would if you were a new customer — or cashing in an upgrade — with one of the major post-paid carriers.

Leap customers would need to pay $499.99 for the 16GB 4S (Apple charges $649 for an unlocked 16GB 4S). An 8GB iPhone 4 is also being made available for $399.99.

You also only get access to Leap’s 3G network. Depending on the current network availability in your neck of the woods, that may not be a change.

If you’re interested, the company starts taking pre-orders June 15.

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