I don't mind the reason for it, but I still think the 4 letter extension is awful for cellular phones if you don't have a blackberry with a full keyboard. With a standard phone keyboard, I have to press "6,pause,6,6,2,2,4,4,4" just to enter "mobi" on a 10 key phone pad. a better tld for a cell phone would be something that could be typed with only 2 or 3 keystrokes such as .pd (Portable Device) that could be enter as "7,3" or maybe .pdw (Portable Device Website) as "7,3,9",
I know some kids are pretty quick at typing text on a 10 button keypad, but some of us old dogs don't want to learn new tricks. Disregard this rant if you have a blackberry device with a full keypad or think evenyone will have one soon.