i would check these two links. the first one deals with defaulting to the home tab after putting into sleep mode, and i believe the second one will lead you to a tweak/fix for in call defaulting.
http://forum.ppcgeeks.com/showthread.php?t=82944
http://forum.ppcgeeks.com/showthread.php?t=78019
you should be able to find more info in those links. i have not encountered this yet so i do not have any experience to share, sorry