When you enter your base and walk to your bed, you can save. I forgot the stuff about Wonder Mail, though.
You do not know what you are talking about.
PMD: RRT does not save on gpSP. (The GBA Emulator for PSP)
You will ALWAYS get a "Save Failed" error message in-game when you save.
I am currently trying to find a way to fix this... I might have found something though, still searching the forum to be sure.
EDIT
oopsies, didn't mean to thread revive
I believe it should work the same way as it being for GBA just go to the bed and click to save -_-'
i think the only solution to this problem is that make an update of gpsp that can read flash128 save files...... because now i can save my game in vba in flash128 format