According to the latest fare/flights load at CO res, CO will be operating its 737-900's between IAH-CZM (eff. Jun 14) and IAH-PVR (eff. Jun 24)
14Jun01 CO 1209 Departs IAH 0924 Arrives CZM 1134
14Jun01 CO 1204 Departs CZM 1245 Arrives IAH 1434
24Jun01 CO 1741 Departs IAH 1150 Arrives PVR 1423
24Jun01 CO 1740 Departs PVR 1520 Arrives IAH 1744
Thus far, these are the only 739 origins/destinations I've seen, however I'm sure as the CO route planners continue to 'tweak' the schedule, we'll see these 739's to other destinations, possibly EWR-TPA, MCO, FLL.