ok now the DS has the R4 right, anything similar available for any gameboys? mainly gba and sp
so i can have a bunch of games on one cartrige? even if its using SD or micro SD? just curious and that, =]

There were many flash cartridges for the gameboy advance, but they can be hard to find now, unless you know somebody who wants to sell one.

ah yeah i remember now kinda, yeah,
how much space do they hold on average and how many games? my mate told me a site to get the ROMs from ages ago, and i know it was legit and a massive load of them,

If you have a dslite I can sell you one for that. (You will need to already have an r4 or any flash device )

Most had onboard storage. The one that I got was the xrom 512mbit (64MB). They advertised megabits, instead of bytes, because there's 8 bits in a byte and they could make it sound like they had more storage. I do remember one or two that took SD cards near the end of the GBA's life.

EFA linker 512mb