This tip will work for Android 4.x phones running Ice Cream Sandwich of all flavors. It works on numbers which you know, don’t know and existing contacts. Between Android 2.x and Android 4.x google changed the procedure. The old way was to long press on a contact and select “add to blocked list”, which also gave you another icon (a blocked list) in the contact list. Google has gotten rid of this.
Unknown Callers: Press on the number and create a contact called “Blocked Callers”. I like to set their picture to an “Do Not Enter” sign but whatever you want. If you have this contact already you can simply press on the call in the call log and choose “add to contact” and then select “Blocked Callers”. Eventually you’ll end up with “mobile 1” “mobile 2” “mobile 3” … and so on but who cares. Now proceed to reading the next part….
Known Callers: Don’t feel like hearing from someone? Open their contact and press the properties button (or menu on some phones). The menu will open. Google added a check box called “All Calls to Voicemail”. You guessed it, it sends all calls from this caller to voicemail until you uncheck it. For unknown callers, I add them to the list and they go into voicemail. For known callers, this is an easy, temporary fix. What if you want all calls to go to voicemail for a particular period?
Turn your phone off.