If you want to use GO Dialer/Contacts as your only dialer app, Here's how.
Install Go Cotacts from Market.
Also install Contact Editor by dmfs, also on the Market. (You'll need this to make contact editing work.
Open Root Explorer.
Navigate to /data/app.
Multi-select the com.jbapps.contact-1.apk file, and com.dmfs.android.contacts-1.apk file move them to /system/app/
Set rw-r--r-- permissions for both apks that you moved.
Reboot your phone.
Now Go Dialer is your main dialer app, and your contacts can be edited