Assuming you want access to more than 32MB of audio files at once, you must store said files within a project on an external drive (USB flash or, as some have suggested, a USB hard drive). The external drive can store as many projects as will fit.
When you turn on the Fantom-G, it automatically accesses the last active project, and automatically loads all samples stored within that project to the Fantom-G's internal RAM. All samples and audio tracks must exist in RAM for you to hear them.
RAM-based audio has numerous advantages, but it also has its disadvantages:
• Load times can be a pain, as everything has to be transfered to RAM.
• Traditional cut/copy/paste DAW editing is next to impossible, because the song's timeline is basically just triggering samples. This isn't a pointer-based system like other DAWs and standalone digital multitracks, which tell the processor to play specific parts of non-local files at specific times (and require much faster media than what flash memory typically allows).
• There will be a limited amount of memory available, as modern RAM capacities are always smaller than storage (hard disk) capacities.
So the Fantom-G is, by definition, not a DAW, because it doesn't have pointer-based audio tracks. But that's fine, because I don't think Roland's interested in throwing a VS-2480 into their keyboards. The G is an instrument first and foremost, and tracks that can be instantly triggered, timestretched, and pitch-shifted make more sense in this regard. It'd be insane to try to make the Fantom compete with the Apples and Digidesigns and Microsofts out there.
Now admittedly, Ableton Live can pull off a lot of this, because it treats audio a bit differently than Logic, ProTools, or Cubase. I believe it uses a much larger RAM buffer for one. But it's still not an all-inclusive hardware instrument.
Assuming the Fantom-G's USB Memory port is USB 2.0, Roland could possibly add HD pointer-based audio from a non-local volume, but it opens a TON of worms—one of which is "what happens when you change the tempo of a song?" Wham! Your tracks are out of sync, but only the HD audio tracks—your MIDI and RAM audio tracks are locked in. How do you explain that to newbies?
I do, however, wish Roland would allow realtime bouncedown to HD, like in the MV-8000/8800. It might be a bit weird, considering some flash drives might not be fast enough, but it's certainly doable with the right media.