Configuration menu -> instruments -> settings -> connection -> internettelefone create new profile (gismotel)

Configuration menu -> instruments -> settings -> connection -> SIP-settings create new SIP profile, settings:

profilename: gismotel
serviceprofile: IETF
standardaccesspoint: (your own access point ssid)
public username: sip:7xxxxx@sip.gismotel.com
(use your gismotel account 7xxxxx)
compression: no
registration: yes
use security: no
proxy server
proxy serveraddress: sip:sip.gismotel.com
securitydomain: sip.gismotel.com
username: 7xxxxx
password: xxxxxx
free routing: yes
transfertype: UDP
port: 6060
registrar server
proxy serveraddress: sip:sip.gismotel.com
securitydomain: sip.gismotel.com
username: 7xxxxx (use your gismotel account 7xxxxx)
password: xxxxxx
transfertype: UDP
port: 6060