Today I received a question in our comments section about the Text message memory full error message that seem to be common on the Motorola Droid these days. When you are receiving this message, you won’t be able to receive text messages.
The problem is likely happening because the Droid is out of internal memory space. The Messaging app doesn’t use SD card storage space to store messages. It uses the internal memory where apps and app information is stored.
To free this space up and prevent this message, you can navigate to Settings > Applications > Manage applications and uninstall apps you don’t need, or move the apps to the SD card. Doing this with one or two apps should provide enough internal memory space to receive text messages again.