If you want to use Hoockflash Control with the “R”-Button on a Gigaset phone connected to a ATA191, you probably need to change the Hookflash Timers on CUCM to get this working. Otherwise, the “R”-Button won’t do anything.

Refer to the following settings on the Phone configuration of the ATA191.

This ATA was a replacement of a ATA186 which was registered through SCCP. With the old ATA it worked without any changes on the default configuration.