I read about this issue on other forums and it appears that speed dial is one of those things that JB deems not important. I don't know, I have the side loaded unofficial version of JB, so maybe the official OTA JB will have speed dial. Anyway, people are looking for alternatives such as separate apps like Speed Dial Pro etc. Good luck.
Drag your phone icon off the bottom row and delete it or place it somewhere else, and put your Go Dialer widget in its place. Go Dialer will give you the functionality that you had before, and speed dial works with it. To set up speed dial numbers, use Go Contacts.
I was not happy with losing speed dial. But, I'm adjusting to the "replacement". I opened up a space on my normal home screen, went to Widgets and dragged Direct Dial over to that open space. when you release the Widget it opens up your contacts and you select the contact/number you want. It puts the contact in that spot. Then, you can keep doing this for all of the numbers you used in speed dial. They stack on top of each other and form a sort of folder. When you tap on it all of these contacts open up in a window and just tap on the one you want. It actually works much better than speed dial. The reason I say this is that now you can see the contact names/info instead of having to memorize numbers. It works for me! Now, if I can just find an app for WIFI. My USB tether does work though since JB.