[Frage] Was macht der Befehl AT+CFUN=0 mit meinen UMTS Stick

This command selects the mobile station’s level of functionality.
When the application wants to stop the product with a power off, or if the application
wants to force the product to execute an IMSI DETACH procedure, then it must send:
AT+CFUN=0 (equivalent to AT+CPOF)
This command executes an IMSI DETACH and makes a backup copy of some internal
parameters in SIM and in EEPROM. The SIM card cannot then be accessed.
If the mobile equipment is not powered off by the application after this command has
been sent, a re-start command (AT+CFUN=1) will have to issued to restart the whole GSM
registration process.
If the mobile equipment is turned off after this command, then a power on will
automatically restart the whole GSM process.

The AT+CFUN=1 command restarts the entire GSM stack and GSM functionality: a
complete software reset is performed. All parameters are reset to their previous values if
AT&W was not used.
If you write entries in the phonebook (+CPBW) and then reset the product directly
(AT+CFUN=1, with no previous AT+CFUN=0 command), some entries may not be written
(the SIM task does not have enough time to write entries in the SIM card).
In addition, the OK response will be sent at the last baud rate defined by the +IPR
command. With the autobauding mode the response can be at a different baud rate, it is
therefore preferable to save the defined baud rate with AT&W before directly sending the
AT+CFUN=1 command.