I was told by Nokia that in America the Nokia 6230 can use a 128 MMC w/o any problems. Anything bigger than this is can only be used in other countries, but if you upgrade the phone's firmware to V.4.43 then any size MMC can work. Without upgrading the phone's firmware then what happens is alot like a home PC, things just start to go haywire, this is usually caused by putting something in the phone that the phone doesn't recognize or support and of course the end results are whatever can happen will happen.