When my sisters or I call my parents, there are many times my dad isn't quite sure which one of his four daughters is on the other end of the line. Mom is a little better at discerning the source of the voice. I know my husband's parents sometimes aren't sure if it him or his brother when he calls. And yet we all know each other quite well, obviously!
How much more important is it for us, then, to be aware of God's voice when He speaks to us? How can we know His voice is speaking to us if we aren't in the habit of listening? Adam and Eve knew the sound of God "walking in the garden." That seems to be a pretty intimate relationship, doesn't it--to know the sound of someone's movements.
I have been told that the best way to know a counterfeit is to study the original. Bank tellers are trained to spot "phony" money by studying the real deal, and memorizing every detail. The best way, too, for us to know God's voice in the midst of the clamor of voices trying to capture our attention, is to spend time with Him more and more, and listening to Him. The more we listen, the better we will know His voice. The better we will be able to hear His calm assurances, gentle proddings, challenges to holiness, reminders of what we know...
"My sheep hear My voice, and I know them, and they follow Me."