Android - Can I use 2 android phones as walkie talkie? (without internet!)

Here is what I use that do not need an internet connection:

https://play.google.com/store/apps/details?id=com.androidintercom

https://play.google.com/store/apps/details?id=com.remaller.android.wifitalkie_lite

The project mentioned by BobFlemming is the Serval project, and they are also on twitter. The android application will be available soon apparently.

Thought I'd mention because not entirely straightforward to find it through the youtube link and that the twitter account isn't advertised on the site. Also I cannot +1 or comment yet so adding it as a reply.

Its been tested by a group here:

http://arstechnica.com/gadgets/news/2011/01/researchers-enable-mesh-wifi-networking-for-android-smartphones.ars

So it is possible.