RESEARCH TRIANGLE PARK, N.C. – AT&T Wireless, Apple’s service partner for the iPhone, says the new iPhone 4 can be pre-ordered on June 15.

The first phones will be available on June 24 through home delivery.

Apple CEO Steve Jobs Monday at the company’s annual developers conference.

AT&T also said customers who are eligible to upgrade their phones through existing contracts this year can upgrade this year.

The iPhone 4 16 gigabit version is $199 for upgrade eligible customers.

The iPhone 4 32GB version is $299 for upgrade customers.

If you’re a current AT&T subscriber, the company applies a secret formula to determine if you’re eligible for the new-subscriber price.

If you’re not, you’ll pay $399 for the cheaper phone or $499 for the one with more storage.

What’s new this year is that AT&T is being more generous about applying the formula. If you would be "upgrade eligible" at any time this year, you will be allowed to buy the iPhone 4 on the launch day for the low price.

This means a lot more owners of last year’s iPhone 3GS model will be allowed to upgrade to the iPhone 4 this summer, and AT&T will be able to avoid some of the complaints it endured around the launch of the 3GS.

Factors that go into the eligibility formula include how much you pay each month and whether you pay on time, AT&T says. IPhone customers who spend $100 or more each month on service are generally eligible for an upgrade after they’ve had the phone for between 12 months and 18 months, according to spokesman Mark Siegel. Customers can find out on AT&T’s website whether they’re eligible.

Like other phone companies, AT&T subsidizes the cost of smart phones, and it wants to make some of that money back through service fees before letting subscribers get new phones.

On Monday, AT&T stopped signing up new customers for its $30 per month unlimited data plan, which was required for the iPhone and other "smart" phones. The plan is being replaced with $15 and $25 plans with a limited monthly amount of data. But AT&T will allow current unlimited data plan subscribers to keep it, even if they get a new smart phone.

AT&T also is cutting prices for existing iPhone 3GS models.

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