The 2.3.4 Android iteration lacks the ability to auto reject calls. You can still reject calls with messages, but no more auto reject. There is, of course, an app that can help you out with that.

Android smartphones give you the possibility of rejecting a phone call and sending a message to the caller. This feature can be very useful, when you are driving or doing some important tasks. How ...

Reject with message. There are several ways to auto-reject a text or call with Android, depending on which carrier you use and whether you want to add apps. Android Auto, ...