The iPhone OS platform was built using the knowledge that went into the creation of Mac OS X, and many of the tools and technologies used for development on the platform have their roots in Mac OS X as well. Despite its similarities to Mac OS X, you do not need to be an experienced Mac OS X developer to write applications for iPhone OS. The iPhone Software Development Kit (SDK) provides everything you need to get started creating iPhone applications.

Apple's iPhone 4 is a beautiful device, one of the nicest in the growing field of amazing smartphones on sale this summer.

The software gives its touch-screen controls a buttery smoothness, plus a few handy new features.

Inside is a snappy processor and a new battery that keeps the phone going all day with moderate use.

Apple gave the phone a new case that's more blocky, masculine and Teutonic. It looks like a robot's ice-cream sandwich two slabs of glass with a stainless steel middle.

The iPhone 4 also works better than its predecessors as an actual phone, with dual microphones that help cancel out background noise.

Overall it's a great upgrade for the standard-bearing smartphone.

Which makes it too bad there's an elephant in this elegant, ultra modern room. The iPhone 4 has a glitch that can lead to its wireless signal abruptly dropping if you hold the phone a certain way.

A lot of users may never notice or be affected by this problem.

The stainless-steel band around the case cleverly doubles as the phone's antenna. That helped make the phone thinner - Apple claims its 0.36-inch thickness makes it the world's thinnest smartphone.

Apple also says the new antenna works better than ever. As long as you hold the phone correctly.

If you cup the iPhone 4 in your left hand - which right-handed people do when using a touch-screen phone - it's easy to bridge two sections of the antenna and cause the signal to drop.