What is the storage size of MMC you using now?

512 MB , but u need to have a memory card reader as well.

N-gage don't support 512 MB or bigger MMC ?

Yes i am using a 512MB, but the n-gage can only support up to 128MB problem free. Any problems u may have with a larger memory card can be sorted with a memory card reader. I have heard of people using a 2 GB memory card befor.

Also does anybody know if the QD can support a larger card with no problems?

no, I am using 256MB for my N-gage now.

The largest capacity MMC is 1GB.The MMC slot for all Nokia(maybe all) Series 60 devices is identical.If the N-Gage can use it,the QD can also.

The N-Gage does support MMC's with higher capacities then 128MB,Nokia doesn't.Search the forums,this has been discussed more then once.