Star Trek Online is taking a slightly different approach. The upcoming overarching currency dilithium can be traded for Cryptic Points via the new dilithium exchange service, which has just gone live on the Tribble server for players to test. But the trade isn't a straight one, instead working on an auction-type system.
The newest Path to F2P blog outlines the means for players to use the exchange system, which works both ways -- players can look to buy dilithium or Cryptic Points and are able to browse the overall market and see what other players are offering or asking. It's not quite as simple as being able to swipe your credit card and then grab some in-game money, but it's certainly blurring the lines between real currency and game money.