A free program for Android, by agent-hp.
WiFi Phone allows you to call other Android users in your vicinity using your phone’s WiFi connection. You don’t need to be near the other person to make a call, nor do you need to have your phone connected to the Internet. You can use this app to call people up to 100 meters away from you, which is quite good for making phone calls in a place with bad reception.
WiFi Phone supports both Wifi Direct and the standard phone call function. The app can be used with either of these two connection methods. You can also turn on/off the speaker volume using the hardware buttons. The app does not collect any data about you or the people you contact.