I'll try to answer this the best I can:
The chances of getting pregnant on the pill aren't very good (if you take it correctly, you've get less than a one percent chance with most oral contraceptives). I've never heard of a pill just not working. Many times if someone gets pregnant while on the pill it is because they have taken it incorrectly, like missed their three hour window to take it, skipping pills, etc. However, manufacturers warn women not to take the pills if they are pregnant for the risk of birth defects.
EC (emergency contraception, AKA the "morning after" pill) and birth control are, in essence, the same thing. EC is just a much higher dose of hormones that what is in BC. You can actually use BC pills as emergency contraception if you know how many to take and don't have access to EC. However, not all brands are approved for use in an emergency.
[This message has been edited by JamsessionVT (edited 12-03-2005).]