I was having issues mounting my D1 SD card on the D3. I figured i would share the info I found.
I apparently made the mistake of trying to clear off the SD card before attempting to mount it in my D3. I only wanted to transfer my photos and other random files, not all of the apps and such stored on it.
Well, If I booted the phone with the card in the SD would not mount. I tried to mount it and got an error in the status bar which lead me to a format option. I tried that but it would never work. The format option in the main storage configuration area would also not work.
Come to find out, the way to get the D3 to recognize a card in this state is to insert the card with the device on. I was a little scared to try it, but it worked fine. I was given the prompt to format and it worked and now the card is recognized.
I hope this helps others.