I actually got this working. You have to telnet into your router with serial cable via eth4(I got mine with the router). Then once in there you have to delete the software on your router. You will have to be in config mode for this.
Oh yes, you need the recovery software found on the billion website for you specific router. Once you have deleted the software, you will have to boot it into recovery mode, where it will load the firmware that you specify when recovering. Be careful though cause you have to be exact which version you have. I did this like 2 years ago, but thats exactly the way i did. I had the modem for 2 weeks and had to get it open.
BE VERY CAREFUL, READ THE ROUTERS RECOVERY DOCUMENT ON HOW TO EXACTLY DO THE RECOVERY. IT MIGHT BREAK YOUR ROUTER.
It took me about 3 hours to figure out. I don't have that router anymore though, so unfortunately i cannot create screenshots or tut. I will try to get my friends old 1 to create the tut.
yo cn u pm the steps i really want to unlock this router