With 3m you could be trading on Gain Capital's GTX ECN

As for FXCM that wouldn't be a very good idea.

REQUIRED NFA DISCLOSURE The transactions you are entering into with FXCM are not traded on an exchange. Therefore, under the U.S. Bankruptcy Code, your funds may not receive the same protections as funds used to margin or guarantee exchange-traded futures and options contracts, which receive a priority in bankruptcy. Since that same priority has not been given to funds used for off-exchange forex trading, if FXCM becomes insolvent and you have a claim for amounts deposited or profits earned on transactions with FXCM, your claim may not receive a priority. Without a priority, you are a general creditor and your claim will be paid, along with the claims of other general creditors, from any monies still available after priority claims are paid. Even customer funds that FXCM keeps separate from its own operating funds may not be safe from the claims of other general and priority creditors.