SMS Texting with a Phone Number
Though the DSi has no native SMS or cellphone support, it does allow connection to the Internet. You can use this capability to enable SMS chat. You will first need to download and install the free browser from the DSi store. You then enter "www.google.com/voice/" in the browser search bar navigate to the Google Voice website. From there, you will need to set up your free account. If you have a cellphone, you can use your existing number or alternately choose an available phone number from your area code. Once you connect to Google Voice, you can send SMS text messages from your DSi to a cellular device or receive them to the screen of your game console.
Social Network Texting
As long as you have access to a wireless Internet connection, you have access to a host of text message features. Using the DSi browser, you can navigate to mobile versions of your favorite social networks such as Myspace, Facebook or Google Plus. You can use any of the DSi's various input mechanisms to send text messages, either via touchscreen keyboard or text recognition. You can send the text via message or using the chat features of the social site. Some sites, like Facebook, allow you to directly upload images from your DSi with your text content.
Pictochat
Perhaps the easiest mechanism to send text messages with the DSi is the Pictochat software built in to the DSi. This handy application allows you to create your own chat rooms, join existing ones, or send messages to friends. With the DSi's wireless capability, you can connect with up to 15 people at once. Because the software also allows support for directly drawing on the chat screen and using custom characters in addition to text, you can use Pictochat for drawing games as well as normal chat.
Conclusion
While the DSi will never be a substitute for the convenience of a cellular device for sending text messages it makes a passable choice for messaging as long as you have access to a network or you are communicating with friends within the wireless range of the device. However, for large public events (like concerts or conventions) the DSi may actually a better choice than a cellphone. The capability to add drawings to your texts is very useful to clarify confusing directions, and the ability to type or write instead of using numeric key entry makes the process simpler. Finally, the DSi's wireless messaging is virtually instantaneous as opposed to SMS, which can be finicky or slow depending on your connection.