After learning that customers have been complaining about its upgrade policies regarding the ready-to-be-launched iPhone 3G S mobile phone from Apple, AT&T announced on Wednesday that it would offer special prices for the existing iPhone users on its network. According to the carrier, those who already have an iPhone will be able to upgrade to the new model at the same prices that new buyers benefit from, as soon as the device goes on sale on Friday.

As many of you might already know, AT&T previously announced that current owners of an iPhone who would like to upgrade to the new model would have to pay $399 for the 16GB model, while new buyers were asked only $199 for the new iPhone 3G S. Given the fact that the Dallas-based carrier heavily subsidizes the purchase price of the phone, it was not prepared to enable users who hadn't “paid off” their old phones to purchase a new one at the same low price as new customers.

Even so, it seems that the wireless carrier has changed its mind about the offering, and will allow existing customers to upgrade to the new iPhone 3G S 16GB model, only that they should meet certain conditions. First of all, those who pay at least $100 a month qualify for a “new buyer” price after 12 to 18 months, AT&T says, yet those who qualify for the lowest price by September will be able to acquire the new device at the “new buyer” price on Friday.

The carrier says it took into consideration the fact that the most recent iPhone model, the 3G, became available for purchase only 11 months ago, which means that even those who acquired it at launch won't qualify for the lowest price on the new phone. While announcing the new upgrade policies, the company also mentioned that it would automatically adjust the prices for eligible customers who had already pre-ordered the new model online, so as to make everybody happy.

Of course, there are always those who are not eligible for an upgrade, which means that they will have to acquire the new iPhone 3G S at the already announced prices, $399 for the 16GB variant or $499 for the 32GB model. At the same time, there is also the full-retail option, which will require $599 for the 16GB iPhone 3G S and $699 for the 32GB version. Those who would like to purchase the device at a lower price but are not eligible for the upgrade just yet will have to wait a little longer. The upgrade eligibility can be checked via this link.