Call recording works, voicemail etc yes.
You can modify the system however you want, use a USB Mass storage device, or record to the spare space on your 4 GIG SD card that hosts the system, create alternate mount points jus where voice recordings are saved, or even use a NFS/Samba mount point to a network server - or store them local and have a daily cron task move files aged more than one day off the system onto a network server.
Endless possibilities, the only limitation is your imagination and skills

After all. Its unix.