Outgoing calls, the dialer is in contacts, drawable_hdpi and drawable_hdpi_finger.
In call, the dialer is the phone apk, but usually when I try doing that with ninja morph the phone and contacts disappear so either use something else to theme that part or find a rom with an in call dialer that you like. I still play with them some but am getting tired of reflashing a rom and theme to get my phone back.
ninja morph doesn't like it when you try to theme pretty much anything other than notification bar icons. i tried NMing widgetlocker and it didn't work. what i think you have to do is use Root explorer to do it. copy the contacts app out of system/app, and paste it to the SD card.
once there, you can use root explorer to copy and paste the new images into the .apk. once this is completely done, you have to mount DATA/app folder r/o and paste the modified .apk into system/app and change permissions to rw-r-r, reboot and you are done.
i always make a backup when i do this tho, b/c if i do mess up i always have that to fall back on.
this is the method i used to change widgetlocker, which is a downloaded app and not a system app so i dont know if it will work for sure.
you can always create an update.zip file to do all the work for you.