its not only a rim problem.
devices are made interesting.
most devices today in 2009 are made with 256 ram, this goes for droid, iphone, blackberry, windows mobile.
then comes storage.
while an iphone can hold 8/16/32 megs of apps, it can only run on 256 ram.
most phones, less the iphone only use ram, which means loads os/apps its were its stored in.
some offer running off an sd card, but this brings up data bus speeds, ram cards read writes and slow downs.
most phone mfg really dont gear to compete with lets say psp/ nintendo ds or other portable video game system.
most phone offer space for 3rd party functions of communications. where it be im, facebook, myspace etc.
the problem with sd cards is class of card, read/write etc and lag.
now adding flash ram, or Flash EEPROM ram to a device in large capacity 8/16/128 gb is possible but, these devices will only run the apps in 128 / 256 ram.
sorta like your pc, you have a limited amount of ram where programs run before the os swaps the unused to disc.
the mobile market of a phone still needs does not have the hardware, or cpu /gpu power to offer an actual mobile platform to do both right.
with the new snap dragon/ tegra video grafix for smart phones and crappy batteries is it worth it even to offer a device that dies in 30 min?