A humorous comment that accompanies the article says, "Oh yeah, I remember those, we called them pagers."
And while I'll admit that I kind of like the idea, I can't really see the need when most smart phones can either go directly to the site or have various Twitter applications. But I also have to think that there are some people who may prefer this over the higher costing smart phones.
The device called a TwitterPeek is available exclusively from Amazon, which also sells the Peek Pronto Mobile Messaging Device

Peek Pronto Mobile Messaging Device with Lifetime Service Included (Grey)