What type of memory cards I can use in 3660 and up to which size?
Memory card in 3660
MMC, MultiMedia Card. Nokia supports up to 128MB officially, but there are reports of people using 256MB, 512MB and even 1GB MMC cards. Search the forums and you will find plenty of such discussions: http://www.allaboutsymbian.com/forum/search.php
Note: SD (Secure Digital) cards may look like MMC, but they aren't. Devices that take SD can usually also take MMC, but MMC-only devices like Nokia phones only work with MMC.