From my experience with Deutsche Telekom (DT), here are my notes for a working SIP trunk (not PJSIP) configuration:
there is a DNS resolving problem (add the record to the hosts file):
217.0.15.67 sip-trunk.telekom.de
*****
Duetche Telekom Supports TCP only and user phone:
host=sip-trunk.telekom.de
defaultuser=551234567890
secret=xxxxxxx
type=peer
port=5060
fromdomain=sip-trunk.telekom.de
fromuser=+4981234567890
canreinvite=no
insecure=port,invite
disallow=all
allow=alaw&ulaw
session-timers=refuse
qualify=yes
transport=tcp
*****
register with tcp and phone as user:
tcp://+4981234567890:xxxxxxx:[email protected]/+4981234567890
****
We need to activate dns srv lookup in sip.conf
sip-trunk is used for telekom sip trunk agreements. (Basic number with extensions, earlier called ISDN Anlagenanschluss) and can be used from any dsl/vdsl location). tel.t-online is used for single connections, single numbers (Telekokm all-ip, earlier MSN, Mehrgeräteanschluss) and works from the DSL/VDSL connect where it’s contracted to --only (!), with no real need to send legitimation. So everything works.