I bought an iPhone in the first few hours they were available, and I expect to do it again when the iPhone 3G ships next month. But what's the plan for current iPhone owners to upgrade to the iPhone 3G? Will we get a discount? Will we have to renew our service plan from AT&T? What can do we do with our current iPhones? Apple isn't talking about that just yet.The Apple support forums have some answers. I don't know if they're true, but they're answers:

wlcunningham says he talked to an AT&T customer service rep who said if you bought your phone on or after May 27, 2008, you can exchange your 2G iPhone for the iPhone 3G before Aug. 1. You'll get a refund of the original purchase, minus a 10% restocking fee, and then they'll sell you the iPhone at the new price.

Between July 11 and Aug. 1, go to your local AT&T store. Be sure to have EVERYTHING that you had with your original purchase. (Charger, Dock, Book, Original Box and Receipt.) Phone MUST BE in like new condition in order to be eligible.

And if the iPhone is out of stock when you go to the store to upgrade, you're out of luck.

wlcunningham says he doesn't know what happens to people who bought before May 27. "I skated in by the skin of my teeth as I purchased and activated mine on the 27th," he says. Looks like this is wlcunningham's lucky day.

Current iPhone customers will need to sign a new two-year contract. Good news there: "If you are already in the middle of a 2-year contract with AT&T, it will start over upon the purchase of the new iPhone, and not stack on top of itself," says Shurst, commenting in the same thread.

Saul Hansell, writing on the New York Times Bits blog, has an interview with Ralph de la Vega, chief executive of AT&T Mobility:

Current iPhone owners can upgrade now, but then they'll be locked in. Because the first iPhone was sold without an upfront subsidy, current users are welcome to buy a new $199 or $299 3G iPhone.

But there are catches. First, they will have to agree to the new $30-a-month data plan, replacing the $20-a-month plan associated with the first iPhone models. Also, they will then be locked into a two-year contract and, as with most subsidized cell phones, they won't be able to upgrade to a new phone at a subsidized price until their contract nears expiration.

So if you think you may really want next year's iPhone, you may not want to upgrade now.

But all of the preceding is hearsay. An Apple spokeswoman said the company doesn't have any information on upgrades. I left messages with AT&T, they didn't get back to me. We'll keep looking into this to get an answer.

If you're just interested in upgrading the software and you're not interested in upgrading the new hardware: Don't worry about it. The iPhone 2.0 software will be pushed out automatically to existing iPhone users in early July, and then you'll be able to start installing native, Apple-sanctioned third-party apps on your iPhone.