I have just published WhoIsIt 1.3.3 to the Market. This version hopefully addresses the "Silent" issue that some users with the Samsung Fascinate (and maybe other models) were experiencing when trying to assign a custom ringtone to a contact. If you are experiencing this issue, try going into the WhoIsIt preferences and checking the "Contact Ringtone Fix" checkbox. After checking this, try assigning a ringtone to a contact and see if this resolves the issue.
Additional changes in the release include:
Phone call announcements now stop as soon as a call is answered.
Added option to display "Invisible" contacts. This may help some users that were not seeing all contacts within WhoIsIt.