The T-Mobile G2X is a variant of the lg-optimus-2x device. Its specifications differ slightly from the original device. According to GSMArena 1, 2, it offers less frequencies for 3G (but higher transfer rates). Both devices originally shipped with Android 2.2 (Froyo). While the original Optimus received official upgrades up to Android 4.0 (Ice Cream Sandwhich), the T-Mobile variant stopped at Android 2.3 (Gingerbread).
T-Mobile G2X (source: GSMArena)