How to use your Cellphone for voice, video, and chat when cell service is DOWN

After using  Linphone from the post HERE , I realized how simple it would be to create a ad hoc phone, video, and messaging network with just a wireless access point and smart phones loaded with the Linphone application. The basic recipe is one wireless access point like an old Linksys and two smartphones with Linphone loaded. The two smartphone will need to join the Linksys wireless network. The Linksys does not need to be connected to the Internet. The two smartphone will basically just be on the local wireless network offered by the Linksys. The only catch is you do need to know each others IP addresses to communicate. Once you know that you can call each other by just using the SIP address in the form - name@IPAddress:5060 the name can actually be anything (e.g. Bill@192.168.1.50:5060).

What this means is that if you take a old Linksys Access Point and run it off a battery and maybe put it up on a mast in the air say 20 to 30 feet up you could provide voice, video, and chat capabilities to a parking lot full of people. This may be useful for an emergency situation, etc.

If the WiFi setup included a registration process, perhaps a directory could be populated so people joining the network would "see" the other members.

I am looking at a Raspberry Pi image that can run as an Access Point, this would then allow a web server to be part of the network. Also the Rasp Pi is small and light and should use less power than a old Linksys wireless router, will need to verify.