Extension on your Phone.com account may have SIP devices associated with them.
The Device API provides information about those SIP devices, such as the SIP credentials required.
The Create Device API allows you to add a Generic SIP device. You may use the extension API to associate the device with the extension, which is required for the device to be operational. NOTE: If you use the Create Device and at the same request, ask to associate the device to an extension (using the "Lines" Param). The Call Handling Rules (CHR) of the Extension, if existed, will be deleted.
To ensure proper operation of the SIP device, you must add some call handling rules to the extension. Adding CHR is usually done by using the extension API.