According to Gartner, mobile gaming revenue is on pace to grow 50% this year alone. That's a worldwide number, though. In the U.S., the numbers are still fairly modest, with an expected revenue this year of $716 million, compared to $4.3 billion globally.

As handsets approach the power of handheld gaming units, these numbers should rise even further. On the developer side, however, mobile gaming faces huge hurdles; primarily, the fact that when a team programs a new game, they have to test it on dozens and dozens of different handheld platforms. Every phone is different, with different screen sizes, processors, keypad layouts, and even the operating system that controls each device. Contrast that with writing a game for the Nintendo DS: if the game works on one unit, it will run on all of them.

All the extra testing on mobile adds significantly to development time, something that's already at a premium, given that mobile games generally don't command more than a few bucks a pop.

Gartner: Worldwide Mobile Gaming Revenue to Grow 50% in 2007 [MediaPost]