The result was a brick. Lifetime warranty or not, the vendor did not honor warranty. Thus I do recommend getting your modem elsewhere. By now, I'd expect OSHW solutions to be available.
Should anybody know how to possibly get past the brick, please let me know. A cursory glance inside years ago didn't yield anything that looked like a PROM.
Ultimately, I'd like the old device I liked to watch the leds blink on to be back alive again, preferably without replacing the whole PCB.
The internal ones shouldn't be much different than externals, they just implement another serial interface.
Would be a pain to desolder and resolder if it's a TSOP chip, but PLCC isn't too bad. You might have some better luck if you high-jack a compatible motherboard's floppy-disk BIOS update process to write a new binary.
56ks are not very expensive to buy off ebay.
If it was a 28f or 29f I failed to locate, I'd be able to very easily write to it; I also can solder/desolder these days.
The next problem would of course be to locate the actual firmware to burn.