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I'm looking for a way to make VoIP calls between two Android devices without having any intermediate server (SIP server) or an Internet connection. Is this possible?

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Why do you want to do this? – unforgettableid Oct 13 '15 at 11:21
@unforgettableid It would be useful in emergency situations try reading this ->… – CrandellWS Feb 1 at 15:54
@unforgettableid "Because it isn't there". This feature is potentially so versatile and useful that not wanting it seems inconceivable. – Russell McMahon Apr 6 at 23:11
@RussellMcMahon: Fair. It could be useful in remote locations, such as a secluded hiking trail or campground where there's no signal available. – unforgettableid Apr 14 at 21:52
@unforgettableid I'm hoping to implement this on phones we use so I can eg talk to my wife "around the property" without making a PSTN call. Serval also allows use of poweramps / external modems in some cases to allow substantrial direct range extension. The phone then is more a useful hardware element in a network than a phone per se. And Open WRT and Serval can be integrated in manners which I have not yet my brain properly acquainted with. .... – Russell McMahon Apr 15 at 10:08

While I've not tried to use my phone like this myself, I found the question interesting enough to do a little googling. The best search term seemed to be android wifi|bluetooth walkie talkie.

The most promising free candidate I found looks to be Android Intercom - direct phone to phone communication over wifi or BT without an intermediary server or telco. The most promising paid for app seems to be WiFi Talkie.

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The OP indicated "without having any intermediate server (SIP server) or an Internet connection" which is going against the OP's requirement and question :) – t0mm13b Jan 11 '13 at 17:08
How is "direct phone to phone communication over wifi or BT without an intermediary server or telco" going against the OP's req of "without having any intermediate server (SIP server) or an Internet connection", exactly? – Logos Jan 11 '13 at 20:46
The linkys to your answer referred to using a Wifi mechanism, the OP did not give any indication of using intermediate server which includes SIP and presumably the OP wanted zero third party support, i.e. no wifi, no internet, no connectivity, no SIP. – t0mm13b Jan 11 '13 at 21:15
BOTH links are peer to peer solutions, though the second one does make use of any local wireless LAN (which doesn't require an internet connection. And you can use SIP without a third party - it's just a protocol, like TCP/IP. – Logos Jan 12 '13 at 2:06
Logos> How do u use sip without a third-party (like a sip server) - any example code? – Jasper Oct 18 '15 at 11:20

The Serval Mesh may accomplish what you are after. It allows mobile to mobile communication simply using the technology available in phones themselves. Also see this question/answer. Note the technology is currently in its infancy and still has many bugs/kinks to work out but the direction is promising.

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Yes :) Use BlueFi Phone or Walkie Talkie Wifi / BT

I used BlueFi Phone. This applications gives you the facility to call another android phone which has already installed this application and within your Bluetooth range or same Wifi Network. You have to add the device which you want to make the call and call directly to this Android Phone without any internet connections.

I think this will fulfills your needs.

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Who talks? Could you please add a few more details (especially links) to make this a useful answer? Thanks ;) – Izzy May 27 '14 at 19:55
Hi Izzy, Please check the details of the answer – Subhojit Mukherjee Jun 3 '14 at 14:03
Thank you very much for the update! Yes, now it perfectly makes sense :) – Izzy Jun 3 '14 at 14:20
I'm getting a "the requested URL was not found on this server" error message on the Walkie Talkie Wifi / BT link. – galacticninja May 1 '15 at 7:44

Yes it is possible and I did it several times. Just install csip simple and create a profile called "user", not linked to any server. To call another person with the same setup, you just need to know his ip address. Once he has sent it via voice, email, sms or whatsapp or ever (much better) a safer way like textsecure, you simply type "user@15.14.173 et cetera (basically user@ other person's ip) and his Csipsimple will ring. It works and it's the purest form of Internet.

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Can you give a link where to find that "csip simple" app? Is it this one? – Izzy Nov 23 '14 at 16:30

You can just install any SIP client and dial in the form user@IP to the other party. Both must be SIP ( any app , do not require to be same app ) But most providers allows you to pass IP-to-IP calls for free and also will allow you to dial other non SIP IP phones ( like Gtalk, Cisco Jabber that is offers for free gateway between SIP and XMPP ( i.e. ) Of course you need some IP connection, Wi-Fi, bluetooch , GSM, 3G ... to do voIP calls, let's say you can't do voIP without IP.

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