Behold the almighty Mil-Spec Geekpurse:

(That's a four-year old photo, so it prominently shows where I used to keep my Palm TX. Don't be fooled! )

It comes with a cellphone pocket (visible to the upper-right), and the N900 slips in easily. I have a lanyard attached so it's easy to remove also.

In case anyone's curious, the Geekpurse is a Maxpedition "Fatboy" Versipack; found it through a Gadgeteer review. I can't stand the name ("fatboy"? c'mon!), but I've had the bag for almost half a decade and have had zero problems. The spool-like thing with the spinning star on the upper-left is a custom key chain reel - I remain my mother's child and so easily lose my keys unless I attach them with something like that.