Using Twitter to Build a SMS Service > Advantages and Disadvantages
Twitter is an attractive option for implementing an SMS service because it's free and comes with a built in user base and social network. You don't need a web server to create a Twitter mashup, either, just a machine with an Internet connection.
On the other hand, anyone who wants to use your service must first become a member of Twitter. This isn't really that big of a deal, though, when you consider that some kind of registration system is required for most services.
The other big downside to using Twitter is that your service must be addressed by name (e.g., "d yourservicename message") on every message, making interactions more complex and arduous. Twitter also takes up a bit of your character limit with reply instructions (but it's nothing compared to the extras 411Sync adds in).