As part of our shift to VoIP, I have the Gigaset C610IP purchased as a replacement for our old Fritzfon 7150, which unfortunately does not work behind a router as a VoIP phone. Setting up the Gigaset is very simple with a sipgate account, since a setup wizard queries the login information and then sets up the access to the Gigaset own. More extensive settings you can make in the clear web interface of the Gigaset. Also behind our Cisco router does the Gigaset unlike the old Fritzfon properly. Voice quality, I can not distinguish from the old ISDN fixed network, it is my opinion as very good. Happily, I can also run my old Gigaset handsets easily with the C610IP. It then function not all comfort functions such as email, weather, etc., but our extensive phone book could be easily transferred from an old handset to the new handsets, really great. I highly recommend this very C610IP, but must add that network knowledge is required in case of trouble (which in old landline phones is not the case, yes, because there are set in these much less).