Earlier this week, we did the math and declared prepaid carrier Cricket Mobile to be the best iPhone deal around, but today’s announcement that Sprint’s Virgin Mobile will also be offering the iPhone 4S starting on June 24th changes the math substantially, and Cricket’s no longer looking like such a good deal.

Virgin Mobile’s iPhone deal requires you to purchase a completely unsubsidized iPhone from them up front at $649, $150 more expensive than Cricket. But that initial money spent up front can really pay off over time, depending on which plan you sign up for.

How much? You can save over $1000 over the course of two-years on Virgin Mobile compared to AT&T, Verizon or Sprint.

Here’s how it breaks down:

AT&T Verizon Sprint Cricket Virgin Minutes $39.99 (450) $39.99 (450) $69.99 (Unlimited) $55.00 (Unlimited) $40 (1200) Texting $20 $20 $0 $0 $0 Data $30 (3GB) $30 (2GB) $10 (Unlimited) $0 (Unlimited) $0 (Unlimited) Activation $36 $35 $0 $0 $0 iPhone 4S (16GB) $199.99 $199.99 $199.99 $499.99 $649.99 2-Year Total $2395.79 $2394.79 $2119.75 $1819.99 $1609.99

A couple notes of explanation. In the above chart, we decided to not nickel-and-dime the big carriers. You can get cheaper plans with Verizon and at AT&T, but these are outlier cases when it comes to usability. We decided that 450 minutes, unlimited texting and at least 2GB of data was the bare minimum service most people expect when it comes to their carrier.

With that in mind, while Cricket’s a great deal, Virgin’s $40 a month plan is a real winner. You don’t get Cricket’s unlimited minutes, but you get more than the big carriers, and you’ll pay almosy $200 less over the course of 24 months than you would on Cricket.

If you’re willing to make do with fewer minutes, Virgin has an even tastier deal: a $30 a month plan that includes 300 minutes, unlimited data and unlimited texting. If you opt for that deal, you can have an iPhone 4S for $1369.99 over 2 years, which is over a thousand dollars less than an AT&T or Verizon plan.

Curiously, Virgin’s “truly unlimited” $50 a month plan is the worse deal compared to Cricket. It actually costs $30 more over two years than the equivalent Cricket plan.

The bottom line? Virgin Mobile runs on Sprint’s network, so it offers service roughly equivalent to Sprint, for budget prices. If you can afford $649.99 up front, this is the best deal on the iPhone 4S pretty much anywhere. These prepaid carriers are going to start drawing blood from the big three, mark my words.