it works the reverse of what you think: you need a list of cell towers, then your gps coordinates to find "nearby" towers. your device will only see the tower you are connected to. at best, if you had dual sims (from different networks), you would see 2 towers.
companies have spent a lot of money compiling lists of cell towers. the device doesn't find the towers; the device finds its own location and compares it to a list of known towers. the better the list, the better the display.
