AT&T has announced that it will begin selling the iPhone 3G in Puerto Rico and the U.S. Virgin Islands on October 17. Pricing will be the same as in the U.S. mainland, with the 8GB model available for $199 and 16GB $299 for new and upgrade-eligible customers; customers not eligible for the upgrade can purchase the 8GB for $399 or the 16GB model for $499. As before, each model will require a new two-year contract. “iPhone will arrive for…