I just got a notification that I can't receive an SMS because "the space/memory was full". Which is it, the internal or SD space, and what's the best way to free it up?
Note - I just installed a bunch of apps, so I'm suspecting it's the SD.
I got this some time ago, and even after deleting all of messages (I back them up to my Gmail) I got the same thing. The problem was that when the internal memory fell below 22M or so (I forget exactly), this message appears. The SMS themselves take up very little space, so deleting them had no effect.
You may also be suffering from this bug, as I was, which it is important to know about: http://code.google.com/p/android/issues/detail?id=4991
SMS messages are stored in your internal phone memory, usually in this location.
Also, if you installed some apps, by default apps are usually installed to the internal memory unless you've specified otherwise ans you're using Froyo or higher or some other variant of Apps2SD etc.
As an aside, try freeing up some space by moving / uninstalling apps that you don't require and clearing up your browser cache and app data from other apps. An app like Cachemate might help if you're rooted.