From FreeSWITCH Wiki

Connecting the Nokia N95 to FreeSWITCH

This should also work for other Nokia SIP capable phones.

It is assumed you have a WiFi access point called 'homeap' defined already and your FreeSWITCH box is at 192.168.0.9 with the default config available.

Go to the main menu, "Tools", then "Settings" and scroll to "Connection". Scroll to "SIP settings".

Create a new SIP profile with the following settings;

Profile name: homefs
Service profile: IETF
Default access point: homeap
Public user name: sip:1000@192.168.0.9
Use compression: No
Registration: Always on
Use security: No

In the proxy server sub menu;

Proxy server address: 192.168.0.9
Realm: 192.168.0.9
User name: 1000
Password: 1234
Allow loose routing: Yes

In the registrar server sub menu;

Registrar server address: 192.168.0.9
Realm: 192.168.0.9
User name: 1000
Password: 1234
Transport type: UDP
Port: 5060

Press back a couple of times to get back to the "SIP Settings" menu, after a couple of seconds you should see the status change to "Registered". Select the profile you just created and make it the default profile.

Go back to the "Connection" menu and scroll down to "Internet tel.". Create a new profile and make sure the SIP profile you just created (homefs) is selected for use with this profile.

That's it. You can adjust the default call routing on the phone in the "Settings", "Call" menu.