After rumors surfaced earlier this week, Virgin Mobile, a seller of prepaid phone service, confirmed yesterday that they'll begin offering the iPhone on June 29. Here's the bottom line: If you go with a Virgin Mobile iPhone 4, you'll pay more money upfront, but over a two-year period you'll save $800 or more compared to a similar phone purchased with a contract from Sprint (provider of Virgin Mobile's network). An 8GB iPhone 4 will cost $549. And service starts at $30/month for 300 minutes, unlimited text messages, and unlimited data.