i read somewhere that sd cards came from development of mmc's & that sd slots can support mmc due to sd cards being slightly bigger. will the n80s sd slot support my n70's mmc then??

http://www.picstop.co.uk/Secure-Digital-(SD)
(site for the sd vs mmc compatibility)

Full-size SD card slots take MMCs. However, the N80 has the much smaller miniSD, where there is no possible way to fit either MMC or RS-MMC cards, even if electrically they could be compatible.