Hey
ECNs are a seperate market that you have to pay to use.
If you trade KO (Last $ 51.54) then lets say
NYSE market BiD oFFER is:
BID 51.51 OFFER 51.57
And BATS market is
BID 51.52 ASK 51.55
Now, if your broker charges a flat fee (No ECN charges) you can buy KO at the offer...