Birth control is a tricky term. Strictly speaking, abortion is a form of birth control, widely used in, for instance, China: it controls the number of births. In another way, so is abstinence: if you aren't engaging in the appropriate activity, you certainly can't produce a child...barring divine or medical intervention!
"Conception control" is really a more useful term, and more in line with the meaning of "contraceptive." Conception control is preventing conception from occurring. Since most (but not all) believe that life begins at conception or later, it skips the "ending a life" phase of the argument for the vast majority of people.
Disclaimer: If you are uncomfortable with a discussion of how different forms of contraception work, stop reading now. 
Conception control would include barrier methods (including the condom, diaphragm, or sponge), the timing of sexual activity, and the use of spermicides in various forms. In my opinion, all three should be treated equally in a discussion of the moral and theological implications.
The "grey area" is those methods which primarily prevent conception but which can, as a backup or side effect, interfere with a fertilized egg or embryo. These include the IUD (which can damage a developing embryo if fertilization does occur), as well as hormonal methods such as "the Pill", the ring, the birth control patch, or Norplant (which is injected under the skin. It would also include the IUS, a hormonal version of the IUD. (That distinction isn't usually made in the US, but it is helpful in a discussion of the implications of the device.)
Most (if not all) hormonal methods work primarily by preventing ovulation, or the release of an egg. No egg, no conception. However, they are controversial because of some of their backup methods: preventing the implantation of a fertilized egg in the uterine wall or preventing the egg from being properly maintained if it does implant. This results in the failure of the egg. (Death of the embryo, if life has begun.) It may also slow the egg's progress through the fallopian tubes, with the intent that the egg will fail before reaching the uterus itself.
The "morning after" pill works in much the same way as standard hormonal methods, except that it isn't used until after sex has occurred. The issues are the same: does it interfere with a life? Different methods act at different stages, so Pastori's latest estimate of eighteen days, for instance, would permit some of these methods.
End disclaimer
I have intentionally left this as a reporting of the relevant facts. I would encourage further discussion on the implications of those facts.
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