RoutIT

...

If you see the correct IP address, than you can go further.

Gigaset T300/T500 settings.

In the Gigaset PBX go to "Configuration" - "Lines" - "Lines" and click on:

Provider settings:

Give the Line an unique name, insert the Registration username <Phone number> and Password. <SIP Password>

...

Use the settings below.

The fromuser field should be the same as the Registration username: <Phonenumber>
The host and fromdomain field are the same as the provider domain settings.

Number Area settings:

Just add the telephone numbers for this SIP trunk. The Country Code and Area Code can be filled in, if different than the default setting.

Extended settings:

To enable incoming calls, you need to use the settings below.

...

Gigaset T300/T500 additional settings.

In the Gigaset PBX go to "Configuration" - "Lines" - "Lines" and click on:

Provider settings:

Give the Line an unique name, set the authentication to: no

...