The 737 community received a bulletin on November 25, 2011.
Although it contains supporting paragraphs, the following paragraph is the salient point...
...The Air Carrier Certificate employed by legacy United Airlines (UALA011A) will cease to operate at 06:00 Central time (12:00Z) on 11/30/11. All legacy Continental and legacy United flights will operate using the certificate currently employed by Continental (CALA014A). Both legacy airlines will file flight plans and operate with “United” flight numbers...
SOC is, indeed, here.