Can I use android phones and PC as walkie talkie? (without internet!) I want to call my PC using my android phone(vice versa) without internet. I think it is possible, but not sure there is a program like that.

PC to Android or Android to PC. Not just Android to Android.

This is not a duplicate of this question
Install SIP user agents on both phones and PC.

You can use SipDroid or CSipSimple for Android and a softphone program like X-Lite on the PC.

Note that you need to set up local accounts when configuring the software. You can then call other parties on the local network directly by their IP:Port.

If you don't want that, you need to install a full blown VoIP proxy like asterisk.