The Mac operating system runs on Apple's iPhones. While the iPhone doesn't ship with any true office applications, it does include easy access to Apple's App Store, where you can find an incredible range of applications--for work and play--available for download.
Smartphones that run the Windows Mobile OS usually come with mobile versions of the Microsoft Office suite, so you can view and edit documents when you're away from your PC. Windows Mobile is available on a wide range of handsets from all carriers, so you'll have plenty of choice in hardware.
BlackBerry smartphones run the BlackBerry OS, which has recently been updated. It sports a newer, more modern look and is easier to use than in the past. Various third-party software titles are available for BlackBerry phones, and with the launch of BlackBerry App World (an on-phone download catalog), we should see even more.
The Palm OS is not widely available, but it retains a devoted following, largely because of its easy learning curve; you'll also find a good deal of productivity software available for Palm OS-based phones.
Every cell phone supports games and comes with a few included, but to expand your collection, you'll have to buy them for a few dollars a pop, and, as with applications, your selection will change by carrier.
This is an increasingly popular feature. Verizon Wireless, Sprint, and AT&T offer their own GPS services while other handsets, like the iPhone, use Google Maps.
There is a dark side, however. Some merchants are capitalizing on the fact that your phone has both GPS and web browser capability and sending advertisements to your phone as you walk or drive by their establishment.