I've now successfully built a compatible toolchain for the Motorola A780, thanks to this good site with instructions.
Obviously, one of the first things to do was to build busybox with a config that enables all the missing tools. For some strange reason, the A780 does not ship with the usual uClibc/busybox combination, but with the straight GNU tools (glibc, fileutils, ...). Unfortunately important bits such as less, top, strace, etc. were missing.
I've also managed to build matching ext2,jbd,ext3,sunrpc,nfsd and af_packet kernel modules. The VFAT partition on the TransFlash card was shrunk, and an ext3 partition added. Some hooks into the startup scripts, and now the ext3 is mounted when the phone is switched on. Some PATH and LD_LIBRARY_PATH mangling in .profile, and I have a very workable environment on the phone.
Obviously the most important goal would be to port the EZX arm architecture support into a recent 2.6.x kernel, and then run a full-fledged 2.6.x kernel on the device. With embedded IPsec, packet filtering, etc. That goal is very far, due to stupid proprietary device drivers.
So for now, I'll be looking into the kernel/userspace API's and the userspace/userspace API's in order to develop native userspace applications that can actually use the phone (i.e. make voice/data calls, use the headset/speaker/microphone, ...