AT&T CL82113 User Manual page 80

Appendix
Adding and registering handsets/headsets
If registration fails, the system will automatically try to register again. If
registration fails after the third try, Registration failed appears on the screen
for a few seconds, and then To register HS, see manual. This may take up to
five minutes to occur. Please start again from Step 1.
NOTE: You cannot register a handset if any other system handset is in use.
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