I tried this on my X1, didn't figure out whether it works on a genuine HTC device, but the principle must be same.
http://forum.ppcgeeks.com/showthread.php?t=118675
The last post of this thread point out that the history part is an addon defined by that registry entry. If it was removed, the HTC dialer may use build-in history list, IMHO.
So I do remove the content of UIExtension entry (BACKUP FIRST!), and the result is here.(No need to modify more than that)
A little ugly...I need to get used to it.
The new history panel works in the same principle as the build-in one.