Log in to your IP Phone.  Follow the instructions here:

Sample configuration of SPA921 

Change and update the following settings that can be found under the "EXT 1" Tab (ensure you have hit the "Admin Login" link)

General
Line ENABLE = yes

Proxy and Regstration

Proxy: End Point Server


Subscriber Information

User ID = SEP Number
Password =  SEP Password

Note:

SEP Number and Password can be found in your Slingshot Dashboard under:

Team Members->Endpoints Page

Ensure that the Type is set to IP