Some interesting data;
(CNN) -- Among U.S. adults who go online, 13% use Twitter -- and more than half (54%) of these people access the popular social media service with their mobile phone, according to new research from the Pew Internet and American Life Project.  - source CNN Tech

 This is interesting as the 13% is based upon adults who go online, nearly everyone has a cell phone and according to this most of those cell phone users aren't paying much attention to Twitter.

The report also revealed some interesting details about the demographics of Twitter users. For instance, 25% of adult African-Americans who use the Internet are on Twitter, as are 19% of Hispanic Americans, compared with only 9% of whites.
Where you live also may affect whether you're on Twitter: About 15% of both urban and suburban U.S. adult Internet users are on Twitter, vs. only 7% of rural dwellers. - source CNN Tech

Don't get me wrong, I thing Twitter is a brilliant and useful idea, however it has obvious limitations especially when compared to SMS and facebook. My opinion is that there can be a terrific synergy in reaching your market with your message by including a simple recipe of Mobile Media linked with facebook & Twitter. It is definitely a good idea to bring some varied value to each outlet in a way that makes sense. It may make great sense for some business and information models to specialize in their media outlets and differentiate and cross pollinate with purpose

For instance Dell Outlet has a great twitter where you may find deals that are not announced elsewhere. Southwest Airlines uses facebook to promote give-aways, garner up to date praise from customers, and share various tidbits about the company and travel ideas. There are both very appropriate uses for these media. Try this Fast Memory Test.