from what I could find between OUI lookups, the pictures of the unit from the FCC PDF's, and their product information, I believe that the X3i/bluetooth variant is manufactured by
USI, and is
this module (the WM-BB-AG-01). From press releases I can find (like
this one) it uses an Agere core for the WiFi.
the internal pictures of the WiFi module of the X3i w/o bluetooth match the pictures in Sychips product literature.