Cell phones provide a great way to be productive on the go. They are also a huge expense if you don't watch it. One girl in Great Britain even had an "injury" due to too much text messaging. As is often the case, all things in moderation.

Staying productive on the go is a prime GTD principle and the use of cell phones is another arrow in the quiver. As my own contract is up in less than a month, I've been gearing up for another round of smartphone study. Here are the contenders for peak productivity:

Apple iPhone: this is sexy and has a magical interface. The con is that it costs a boat-load of money and runs on ATT, which may not be optimal depending on location. With WiFi and the Mac appeal, the iPhone makes any buyer consider leaving their current network and jump ship towards ATT. It's that good.

Palm Centro: this is the cheapest smartphone and latest edition from Palm. With a full keyboard and slim design, the Centro is designed for the "first smartphone" buyer. One con might be its use of Sprint, which as usual is hit or miss depending on your part of the country. The Centro is hip and light and super easy to use.

Samsung i760: while not the sexiest model of our three, this phone has a slideout keyboard and WiFi (always a plus). Best of all, it runs on Verizon which is often the most reliable of networks. A negative is that VW has a ridiculously expensive data package. The i760 is a strong contender nonetheless.

Resources for the road:
Mobile Productivity Toolbox: 100 Resources to Keep You Productive on the Move
How to Save Money on Your Cell Phone Bill
CNET Smartphone Review Guide