So you’d like to add another handset to a base station. Follow the below easy steps.
1) Press down key until the handset menu appears and press “INT/OK” key
2) Press up or down arrow key to select the submenu “Resgister” and press “INT/OK” key
3) Handset display shows “SEARCHING”.
4) Press and hold “page” key on the base station more than 4 seconds until acknowledgment signal is heard
5) Enter the PIN (default setting = 0000) and press “INT/OK” key on the Handset
If the input PIN is correct the registration procedure will be completed with a confirm tone.
After a connection is established the name and number of the handset appear in the display
Note : The base will be ready for registration for 10 minutes when the page key is pressed and held for more than 4 seconds.
Note 2: This works on many cordless phones including Telkom, some Siemens etc.
Credit: http://www.fixya.com/support/t20782172-manual_bell_studio_4200_duo_cordless