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No need for a phone signal for the OS grid ref apps (eg this one) - in fact, however, you MAY have inadvertently hit upon the reason. The what3words WILL need a phone signal as I suspect it works on triangulation from transmitters - it won’t need a GPS enabled device 
pic.twitter.com/oLtbZGGz3u
what3words doesn't require a phone signal to work, it gives your location based on the device's GPS signal.
So it also requires gps and doesn’t use transmitter triangulation...? my question therefore still stands: how on earth does it improve upon or differ from an app that gives an os grid ref that is infinitely more accurate and useful to all?
The beauty of @what3words is how ‘portable’ a location becomes. It is a much easier way of sharing an accurate location verbally. Esp in an emergency situation. But, not a replacement for other tools such as AML etc. Blog post to follow!
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