DIDWW does not support SIP registration as we do not provide termination services. If you have your own SIP server, you can accept incoming calls from DIDWW. You will need to use any of the VoIP Termination services, register your SIP phone with them, and forward calls from DIDWW to your VoIP Provider, that it will ring your device.
Please note, that the most updated list of VoIP providers, which support DIDWW services, you may find here.
Please note, that the most updated list of VoIP providers, which support DIDWW services, you may find here.

How Do I Configure my SIP Phone to Work with DIDWW?