The iPhone may be the only game in town for serious mobile Web developers right now, but that won’t last long. Next year, the iPhone will see some serious competition from Google’s Android platform. Of course, T-Mobile will start selling the first Android phone, the G1 made by HTC, on October 22. But other cell phone manufacturers are gearing up for a major Android push.

The most significant of these may come from Motorola. One of the original partners in the Open Handset Alliance behind the open-source mobile OS, Motorola already has 50 people on its Android team and is growing that to 350, according to an Android developer approached by a headhunter to join the team. That is a huge commitment that shows how big a bet Motorola is making on Android.

This same source has also seen people from Nokia and Verizon at a recent Android developer conference. The conference was put on by Google last week for developers who had not yet seen the G1 to help prepare them for its launch. In general, in order to be an attendee, you had to have an Android app. Neither Nokia nor Verizon are official members of the Open Handset Alliance.

Nokia recently acquired the rest of Symbian it didn’t already own, and is determined to keep that OS as long as possible, since it powers all of its S60 phones. But Nokia may have an Android team sniffing around, which is smart even if it is for nothing other than to gain competitive intelligence. And if Android takes off, Nokia could decide to hedge its bets and launch its own Android phone.

There is a certain inexorable logic behind all the interest in Android.

1. It is a more capable mobile Web computer than anything other than the iPhone.
2. It is a very appealing development environment for app creators—and just like on the PC, apps will drive adoption.
3. Most importantly, as an open-source OS, manufacturers don’t have to pay a licensing fee to whoever controls the OS. Given the razor-thin margins in the cell phone business, that alone is reason for manufacturers to embrace Android (with the exception of Nokia, which owns Symbian). But you can see why Motorola might see Android as the key to its recovery.