In April, Apple reported that nearly 22 million iPhones have been sold worldwide--about 2 million less than the PlayStation 3's current tally. As the multifunctional handheld's installed base grows, publishers are scrambling to port their tried-and-true game franchises to it and its sibling, the iPod Touch.

　　This week, two popular franchises saw new titles debut on Apple's two platforms. 2K Games announced that Civilization Revolution, the latest installment in the classic strategy series from game designer Sid Meier, is now available on the iPhone. Screenshots released by the company indicate the version of the game will be similar to the well-reviewed DS edition, released last summer. Through Wednesday, the game will cost $4.99 on the App Store, after which it will go up to $9.99.

　　For fans of old-school shooters, Duke Nukem 3D has also made its way to Apple's portables. Priced at $2.99, the scaled-down version of 3D Realms' 1996 shooter was ported by Machineworks Northwest. The 20-hour game employs a new engine, which uses a trademarked touch-screen system called TapShoot to allow players to lock onto and dispatch foes.