Is It Possible To Write A New "phone" Activity, And If Yes Then How?

To illustrate the problem, let's say I want to write an app that allows call recording. I know that I can't record the caller and called audio due to the OS restrictions on the sys

Solution 1:

I could be wrong, but I have not seen any phone recorders that work across all platforms because it seems to be a hardware kernel level issue and not an OS/API issue.

As far as replacing system applications you have to root the phone to do that anyway, unless I am misunderstanding what you are asking.

Of course all the android source is available so you can poke around in that all you want and see if there is anything that has been missed

Solution 2:

You can define an activity that responds to the Intent.ACTION_CALL intent, which will cause the user to be prompted to choose between your app and Phone when they do something that initiate dialing a number (the new Skype app does this, for instance).

However, there are some big limitations. You will not be able to intercept incoming calls. And you will not be able to access the API to actually make a call with the phone (again, think of Skype--they handle the intent by placing a call through their own service, not through the Phone's modem).