VS2000 / VS205 handset register to other set

[MANNY]

Hope someone can help. How can I add 2 handsets from a pre-registered VS205 package, to another VS2000 set up.

i.e i my girlfriend wants to use my old VS205 handsets in her VS2000 set up
(my old quad package 1+3 handsets, her double package 1+1, 2 of my handsets are broken so i cant even just swap packages over)

I have tried the
Menu ¬ Register ¬ Base 1 ¬ PIN 0000
(as I have never changed default PIN's)
But all i get is SEARCH 1 displaying
Have tried Base Select ¬ Auto and 1
but nothing

What am I doing wrong? Is the fact that these handsets are from pre-registered packages putting a block on me doing this? If so is there a Firmware reset hack (long outside of guarantee and have two spare handsets to potentially break in trying)
Thanks

[Raistlin]

Moved to 'Fixed Phone Services' as I'm guessing the phones are part of a VM/NTL package, definitely not 'Cable TV' issue though.

to CF by the way