How to set my contacts application as the default?

Is it possible to replace Android's default contacts app? I want my custom app to load in place of the default contact application.

If this is possible, cou开发者_运维问答ld you explain how this can be accomplished? If not, why? The default keyboard can be changed, why not an application?

---

This is for the user to decide. Your application needs to be able to receive the Intent for picking an item from the contact list (see this question). The user will decide then, if he wants to use your application as the default one.