hawaiitech

First, the 7406 guide says to match the handset to the RJ11 jack of the base unit you are using (handset ID 1, 2, or 3).

Press the Options button on the handset
Press Show
Press Next until the display show 6. Handset ID
Press Show to Display the Handset ID (should match the location of the RJ11). Press ok to cmplete or change to correct it.
Enter password will show
if this is a new phone enter the default password, if not and someone has assigned a password, you're out of luck. probably gotta call ITAS or your support people to unlock that.
Sorry I didn't include the default password, but if you don't have it and the handset ID needs to be changed, I would just move the RJ11 to match your handset ID if you don't have 3 phones assigned to your base unit.
Press OK
Display will show Press Digit 1 - 3
Current ID shows on the bottom left, change it from here
Press ok to complete

Then you need to assign a security code
in the options menu, press next until you see 4. Set S.S. Code
The display will show Press 6 digits
Enter a 6 digit code
Press ok to accept

Press next to show 5. Send S.S. Code
Unplug the AC adapter at the base station and plug it in
In 15 sec, press and hold the OK button on the handset for 5 seconds (this sends the code to the base unit).
Display should show Send Ok!
you should hear a beep when finished.

If you get a send error, repeat the steps to send the codes.

goooood luck!