David Beers is enthusiastic about the possibility of controlling mobile devices with a command-line interface. I know what you think - the same I did. You can't possible be expected to learn a cryptic new language to control your telephone! However, his proposal isn't completely off the wall, and he managed to emphasize a few of the great advantages of CLI:s.
First of all, you save time as you don't need as many clicks or button presses to run a command from a powerful CLI as you do from a desktop type user interface. The examples in the above mentioned post uses auto-completion quite aggressively, and when it works well, it requires very few keypresses to make a call, schedule a meeting etc. It should be noted that this isn't about just porting bash to S60. That wouldn't help anyone, as typing is way too hard to use something like that. What's required is a language that's designed to control a phone.
Second, CLI:s don't require diving into data silos (applications) in the same way as you do in GUI:s. To write a message on a regular phone, you have to open the messaging application (click, click), find the recipient(s) in the contacts database (click, click, ..., click), write the message (that'd be the same, regardless of the UI) and finally exit the messaging application (click, click). With a CLI, the whole system is accessible from the same place.
I think a concept like this would require some serious thinking before it has any chance of success. The phone has to be usable by anyone as soon as it's switched on. I don't think a helpful piece of advice, such as "Press 'h' for help" is going to solve that problem. There's no point in developing the next generation UI if it'll only be suitable for nerds like me.
(Background: I grew up with the C-64 (load "file",8,1 ... run), and thought the Amiga was a bit awkward to use at first, as it threw you into a weird landscape of icons and menus intead of BASIC 2.0. I later got used to it, but I still prefer the command-line in Linux, and can't live without Cygwin when I have to use Windows. So I prefer CLI:s, but I can see why not everyone does, and sometimes a GUI really helps.)