Ummmmmm.. NO and YES...
No, if you want this way of eating to work as well as it can.. I would not work my way down to 20 carbs/day. The first 2 weeks of induction is a training period for your body and you will lose a significant amount of weight for a good start to your new life. I believe just as the other posters have stated that 20 carbs seems few.. but when you actually see what all you are allowed to eat and still stay under 20, it isnt really that big of a letdown.

Yes, if the only way you can begin this way of life and stick to it is to gradually drop your carb level down to 20 grams, then that should be the way you do it. But, understand that you will not have the big loss for the first 2 weeks and you will not get many of the benefits as quickly. You will not lose your cravings for food or feel that "non-hungry" feeling as quickly. I don't know how it will affect that first few days of carb-withdrawal. I would assume that whenever you got down to a low level that the withdrawal would start. Be PATIENT through that withdrawal period. It does end and you will feel soooooooo much better overall. So, in my opinion, if that is the only way you can feel comfortable dropping your carb level.. do it. Eventually you will get down to the level that allows you to lose weight.

So there are NO misunderstandings.. I DO NOT think that dropping slowly is the best way and would not personally do it that way at all... but... I believe 100% that low-carb is the way to eat for life and however we can get people to that point is good (in the big picture).