If you want to be able save the password in Office Communicator you must create the key HKLM\Software\Microsoft\Communicator or on x64 OS HKLM\Software\Wow6432Node\Policies\Microsoft\Communicator and set the DWORD value SavePassword to 1.

Now you will have the Save my password checkbox (which will save the encrpted password to HKCU\Software\Microsoft\Communicator\AccountPassword

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