Software Defined Radio Communications
Software defined radio shows quite a lot of technological promise, in the form of HD Radio and a replacement for cell phones, wifi [or wifi-assisted], wireless internet, and could even come as a motherboard card for your box.
It is fortunate that cell phone towers have been cropping up everywhere to some degree, but the manner of signals they transmit are harmful RF frequency signals. Wifi and radio are ~harmless. Digital radio can potentially replace cellular signals, and come in strong even when cell phones get crackly. The same towers can be used to daisy-chain the signal & so can satellites to reach any part of earth or space.
What we need to do is build the signal routing system to get the message from one phone to the other easily and reach the destination in the most rapid and least congested way.
Every phone would relay all signals it received by picking them up ambiently and rebroadcasting them like radio towers. With only a sea of handheld operations, this would not reach far unless correctly tweaked. It might be good to plug the signal into your car's antenna, even via cigarette lighter-out. But if the appropriate array of users lined up, a call could rapidly reach New York from LA in perfect clarity.
If we added the capability of commercial radio towers to the operation, which would simultaneously receive and rebroadcast R-phone signals without affecting their radio signal, [and also going HD/digital radio] that could easily reach all parts of the world rapidly. Include satellites and we've got a deal.
A phone may receive or see an incoming signal and check its own battery life or radio contact mesh and ping whether the signal should be sent through this phone/station. Once a link is established, the ringing begins. Users segwaying signals do not realize they are doing it, because the phone does it itself.
Broadcasting stations can send out numerous signals using many different inaudible sound frequencies all broadcast on the same signal. Pile up data every 25,000Hz within that radio wave and send it. It doesn't cost more or less to speak in a high or low pitched tone on a radio signal. The machine can pick out the correct range and translate the pitch. Multibroadcasting can multiply signal exponentially. See what we can do with that!