Review: Vodafone Sure Signal - Telegraph It works because it contains a 3G transmitter and receiver, like a tiny phone mast in your office. Don't worry, the radiation levels are minimal, no more than a regular wi-fi router. You connect the Sure Signal to your router, in fact, and it then carries the calls, emails and mobile wi-fi through your existing broadband connection. Except I couldn't do this until I'd then connected the Sure Signal and let it configure itself. It did this, flawlessly, in ten minutes. After which I was able to log back into the website and add extra numbers. Each number needs to be registered to access the Sure Signal, but there's plenty of capacity - you can register up to 32 numbers. First time around this registration was done over the phone. Now you manage these numbers yourself online and it's a much easier system. Although you can register up to 32 numbers, only four can use Sure Signal at a time, which may be restrictive for some situations. Best results, it says, are achieved when the Sure Signal is placed centrally and away from items like a wi-fi router. Since it has to connect to your router, you may want to place it as far away as the cable permits (around four feet). Since first launch, when it cost £160, the price has dropped hugely, too, so it'll only set you back £50. Of course, it only works with Vodafone sims (and 3G devices at that), but if that's your telephonic Achilles" heel, this is a great solution. Vodafone Sure Signal 5 stars