Here's an utterly novel concept - you're at home or at an event and you want to get a message to another family member nearby but out of hearing distance. Assuming that they also have a Symbian phone, Wifi Talkie can turn both your smartphones into fully fledged 'push to talk' walkie talkies, at least as long as you're in Wi-fi range of each other. It's slick and it works very well, albeit with a use case that's narrower than Cleopatra's Needle.
Wifi Talkie does a rather splendid job of looking like the device it's pretending to be, a traditional RF walkie talkie. Right down to the screen display (with working battery and Wi-fi signal bars), plus the monochrome LCD:
Apart from the two messages shown above, there's also 'PAIR', shown while one smartphone running Wifi Talkie is looking for another phone running the same within Wi-fi range. The pairing all happens seamlessly and reliably though. To talk to the other person you hold down the central virtual button and chat away, then release it to hear any responses coming through. The magic happens point-to-point, i.e. no router is needed, though this does inevitably mean slightly lower range than you'd expect for normal wi-fi connectivity, since the latter is partially powered by a meaty mains-powered router and larger aerial.
The system works wonderfully well as long as both parties stay within range. There's a choice of audio codecs to use, with AMR being the lower quality one.
In practice, as I say, the use case is somewhat small:
you need to contact another family member or friend who's within 25 metres or so but not within earshot or sight
both of you have compatible S60 5th Edition or Symbian^3-class smartphones
both of you have the Wifi Talkie application running
In practice, most people, losing someone at an event, would just call them or text them. Perhaps the main use case is at home, to pass messages to a family member without having to get up or bother with VoIP or cellular calls.
I don't mean to be too negative - Wifi Talkie is wonderfully programmed and implemented and I'm keeping it for sheer geek play-value, if nothing else!