You don't need to-do anything in 2.7.2. It's all done in 5.2.24 from memory.

Make sure you're using the local ip for the mp40, not the public ip.
Though I think if you are registering them remotely you can use the public ip first then current to local once the profile has downloaded.

You do have your whitelist setup correctly (or disabled).

It's been about 3 years since I've used wevoip on an os7000 so this is all from memory.