* To automatically reject the incoming calls from the specific contact, the simple way is to sent it directly to voicemail. Open the contact with built-in contacts app, press Menu, tap Options and check "Incoming calls" selection.
* Set up a blocklist to block unless calls number. "Mr Number" is a great free android app that blocks suspected spam calls and texts in history, reverse lookup phone numbers, send straight to voicemail and etc. It is easy to use and does lots of things basically.