I wasn't able to assign speed dial keys under 2.2 Froyo OTA. My X is Rooted so I don't know if this problem and fix applies to the non-rooted version. Problem is that if I go to the phone screen menu and select speed dial menu, then select the key, then identify the desired phone contact by searching from it, it will not save that number. However, the fix is to select the desired phone number by scrolling the list, not searching the list. Selecting the desired number after scrolling to it will work. I found this only after a fairly thorough search, so I'm posting this here to make it easier for others.