The CFTC reported that MetaTrader-based broker FXOpen has beeen fined $140,000 for soliciting or accepting U.S. customers in late 2010 and early 2011. FXOpen was one of 14 Forex firms earlier named by the CFTC for soliciting or taking US clients, without being registered with the NFA or CFTC.
FXOpen is rumored (by Forexmagnates) to be doing about $55 billion of volume per month, however FXOpen does not seem to be regulated or licensed by any recognized national regulator, whether in the U.S., Europe or elsewhere.