Once limited to text messaging a targeted message, mobile marketing is now a creative industry about reaching customers anywhere at any time. Thanks to the rise of various mobile devices that are connected to the Internet or mobile networks, mobile marketing is nearly limitless.

AdAge’s Rita Chang today writes “if you think mobile marketing is about reaching customers on their cellphones, you need to get more creative.”

“There are more and more popular devices that are beginning to be connected,” said Eric Bader, managing partner of mobile-marketing agency Brand in Hand to AdAge. “But it’s not, ‘What’s the available media I can buy?’; it’s thinking about how consumers are behaving and what role do devices have in the way they behave.”

AdAge lists four different kinds of mobile devices, beyond the cell phone, that provide opportunities for mobile marketers. How would you market on these mobile devices?

1. E-Readers
(Amazon Kindle, Barnes & Noble Nook, Sony Reader)
Justin wrote a great post last week on “Harnessing The Kindle’s Mobile Marketing Potential.” Now with Barnes & Noble’s Nook competing to be the e-reader of choice, there are plenty of opportunities to market to consumers on their mobile reading devices.

2. Smartbooks and Tablet PCs
There were plenty of deals this Black Friday for tablet PCs, with mobile carriers looking to discount the hardware cost with monthly-rate contracts for data. The always-on netbook may not replace the mobile phone, but as prices come down more and more people will own these portable computers.

3. Portable Entertainment Players
From Apple’s iPod Touch to Nintendo DS, these mini-gaming devices connect to a network and provide ample opportunities for advertising and marketing. Think branded games and you’ll get excited about the opportunities these mobile gaming devices have to offer.

4. Navigation Devices and In-Vehicle Communication Systems
If you aren’t already thinking about how to make the most of navigation systems in your mobile marketing campaigns, you should start. While Android now has Google’s free, turn-by-turn navigation services, traditional GPS companies (Garmin, OnStar and TomTom) are looking to differentiate themselves with even better offerings. If someone is driving around looking for a place to eat or shop, this is the perfect opportunity to send an appropriate and useful message to advertise a nearby opportunity.