BT Synergy 3505? 2 x handsets 3005? how can i fix the problem ?

Press base and hold till beep and then register handset worked for me.

Copeeh
June 2010

Up to 5 handsets can be registered and operated from
any one BT Synergy 3505 base.
With additional handsets, you can make internal calls
between two handsets while a third is making an
external call.
Each handset can be registered on up to 4 bases.
Register handset to base
Make sure the handset is close to the base.
At the base:
1. Press and hold until you hear two beeps (after
about 10 seconds) then release.
At the handset:
1. Press then scroll to REGISTER and press .
The display shows BS 1 2 3 4. The numbers that are
flashing indicate other bases that the handset is already
registered to.
2. Enter - for the base you want to register to,
followed by your base PIN (original setting 0000) then
press .
The display shows SEARCH 1, 2, 3, 4. and flashes
until the handset locates the base.
When the base is located, the handset will be
automatically selected and shown on the display.
De-register handsets
1. Press then scroll to SETUP and press .
2. Scroll to DEL HS and press .
The display shows PIN?
3. Enter your PIN (original setting 0000) and press .
4. Scroll or to select the handset (1-5) you want to
de-register then press .
Display shows CONFIRM?
5. Press to confirm.
Once deregistered, the handset display shows NOT REG.

balistic
February 2009