My only other suggestions to you r to make sure in sipsorcery that you have binded at least one provider and have the register checkmark checked. Set the ATA back to factory defaults, make sure it's unprovisioned, enter the SIP info all over again (make sure the proxy and domain point to 'sip.sipsorcery.com') and reboot the ATA. You should see a green Voip light.
I've had more problems trying to register diectly to providers (i.e. Sipgate, VoxOx, mj via GVout proxy, mj via xGVout proxy but I was always able to register with no problem to sipsorcery and mysipswitch. The ATA VOIP LED would only go out when those servers were temporarily down.
Good Luck,
Synchron