They didn't have Twitter back in the 1960s when Mad Men's Don Draper was defining cool style, but if they did, Don would probably use a Twitter client like this one.
Created by a pair of Ukrainian tech companies, the Tweephone makes you enter your tweets one character at a time using the rotary phone dial. Of course with lots more letters in the alphabet than numbers on the dial, some letters require two or three turns to complete. That means completing a 140 character tweet could take some time, but hey, the world operated at a slower pace back then.
Now let's see if they can build an iPhone that works like a pocket calendar.