Android: How do I customize phone apps menus?

Question

I want to add a new menu or context menu item to existing applications like the Phone and Contacts.

For example, in the contact list, select a contact then you see "Send picture to this person" in the menu. Or from the phone app, while talking to someone, you see a button that says "Mark this call for follow-up" or anything like this.

I've looked at the source code but couldn't figure out how to do it.

Answer 1

The answer is: this cannot be done unless I write a modified OS and install on a rooted phone.