Update: Twe2 is shutting down :-( so this will no longer work.
There's a new website called Twe2 that lets you get Twitter notifications by SMS outside the US (their business model is to add a short ad message to the end of each SMS).
I've been using remember the milk for quite some time now but a lot of tasks were overdue, either because I'm too lazy or because the notifications by mail or even by the gadget I added to my Gmail account were not prominent enough.
So to try and eliminate at least one of the reasons for my tasks not getting done, I set up remember the milk to send my task notifications to twitter and then with the help of Twe2 I get reminded by SMS.
Still have to work on eliminating the other problem though :-)