The operation of the phone is running almost entirely on the color, capacitive touch screen, which although has a very good readability, but unfortunately, only reacts very hakelig. So inputs must often be performed several times before the machine performs as desired this. Since many operations can be performed only via the display and not alternatively using the buttons on the handset, which is quite annoying. Remunerated in the consistently very good voice quality: The respective interlocutor is always clear and background noise such as noise does not occur. I run the Gigaset S820A on the analogue connection of the Fritz box 6360 Cable and works without any problems with a very good sound. The criticized by some other reviewers voice quality I can not confirm definitively.
Conclusion: The Gigaset S820A would normally be thoroughly recommended, unless this would hakelige, annoying touchscreen display. Voice quality, transmission / reception performance and battery life can be nothing to be desired, however, the manufacturer should equip future devices urgently with a well-functioning touchscreen.
Update 25/12/2013: After 8 months of the touch screen of the device is defective, that is, it no longer responds to user input. Since this defect apparently occurs more frequently, you should buy this phone really thoroughly consider.