First off,
You will need to make sure the 69xx phone has the SIP firmware installed to even attempt this. I believe they come with MiNet. You can test this by booting the phone and going to menu advanced, it will ask for a password. Type 22222, If that works its sip.
You will likely not receive any help on this due to this not being a supported setup. In theory it should work. You should be able to web into the phone and fill out the sip information the user is admin and pw is the same as above.
Good luck!