At long last, Apples ever-popular iPhone crossed a major threshold last month, at least in the U.S. On June 22, the iPhone 4 and 4S will officially be offered as pre-paid devices on Cricket Wireless.

So, what's the catch?

Instead of getting a subsidized iPhone for $99 or a 4S for $199 with a two-year agreement, you have to purchase the iPhone at (or near) full retail value. For Cricket customers, that means the 8GB iPhone 4 will sell for $399.99 and the 16GB iPhone 4S will set buyers back a relatively steep $499.99.

When you consider the price and perks of the plan, though, the outright price of the phone is far more manageable. On Cricket, iPhone users will pay $55 per month for unlimited minutes, text messages and data. (Cricket's fair usage policy is 2.3GB.) Versus the upwards of $100 per month with a postpaid carrier for limited minutes and data, it's not a bad deal at all.

However, just this week, we learned of an even sweeter deal. We had heard rumors of a Boost Mobile and Virgin Mobile iPhone quickly following the Cricket iPhone. And on Thursday, the Virgin Mobile iPhone was made official and will launch one week after Cricket's.

What's the difference? For starters, the phones on Virgin Mobile are notably more expensive. The iPhone 4 will sell for $549 (versus $399 on Cricket) and the 16GB 4S starts at $649 (versus $499 on Cricket). These are actually the same prices listed for the same devices unlocked on Apple's site.

That said, the monthly plans start at only $30 per month, versus $55 per month on Cricket. For $35 per month, you get 300 minutes, unlimited messaging and unlimited data (which actually translates to 2.5GB before being throttled.) If you need more minutes, you can pay $45 per month for 1,200 minutes and unlimited text and data, or $55 for unlimited everything. On top of that, Virgin Mobile offers a $5 bill discount to those who sign up for automatic bill payment via credit card, debit card or PayPal.

In other words, if calling isn't important to you and you don't mind signing up for automatic bill payments, you can get an iPhone on Virgin Mobile for only $30 per month.

This is perfect for a secondary line – or in my case, a third line. (Not one I could carry with me all the time.)

I don't need more minutes or text messages, of course. But I can always use more data. Come this summer, Verizon will cancel my grandfathered unlimited data plan unless I choose to never upgrade again. I will simply have to purchase all of my devices no-contract on Verizon to keep unlimited data. In the end, that translates to spending a lot of money so I don't pay outrageous amounts of data overage fees. A lose-lose.

For $30 per month (plus the price of the phone, which I can offset by selling a few of the desk-dwelling phones I currently own), I could have "unlimited" data with Virgin as a backup. That, of course, is actually only 2.5GB per month at 3G speeds before getting throttled. That to me, however, is better than paying for $50 for 5GB of data through Verizon and possibly paying for overages on top of that.

Essentially, the iPhone on Virgin would be used primarily for streaming Spotify and Pandora. And it would serve as a backup, in case I neared my limits on AT&T and Verizon. Is it excessive? For sure. But considering I'm paying $20 less per month on AT&T by not paying for text messaging (and using Google Voice instead) and the price of the iPhone could be easily offset by selling one of my devices I'm not currently using, it'd be beneficial for me to have it as a backup. It's effectively only $10 more per month than I was paying before I removed unlimited messaging from my AT&T line.

When I first wrote about the Cricket iPhone, I did mention data coverage. Cricket uses Sprint's 3G network, giving Virgin and Cricket the same coverage. It's not as consistent as I would like in my area. But for $30 per month (or only $10 more than before), there's little to complain about, especially for a third line.

I haven't decided whether I will definitively get a Virgin iPhone. But I'm seriously considering it. And this is the first time I've ever considered using a prepaid service. For just such a low monthly fee, it's a tough deal to pass up.

How do you feel, readers? Does the Virgin Mobile iPhone for $30 per month seem like a sweet deal to you? Is it too good for you to pass up? Or do you plan on keeping your postpaid line or are you considering other prepaid offers?