This is a good thread, but I didn’t vote because I think both answers can be true.
Interior locution, I think, is very common in people with a deep and advanced prayer life, especially contemplative prayer. (That’s why it’s so necessary that those who have advanced to this stage of prayer to have a spiritual director. I totally agree with *BarbaraTherese’s * Post #13.) I think these people may be less common (but they usually become Saints

).
I think that interior locution is rarer in people who have just started upon the journey of their spiritual life.
Of course, since God is God and can, and will, do whatever is best for us, He may grant the gift of interior locutions to a beginner and withhold it from one more advanced in prayer. As Leonie said (Post #29), sometimes He speaks to our heart even while taking out the trash! (No matter. Whenever and however it comes, it is a great gift!) Actually, I think those are the most real experiences - when it comes out of the blue like that (Leonie hit the nail right on the head in post #33), when you don’t expect it and it’s almost as an “interruption” into our thoughts.*****
In Post #3, *Joysong * writes about the Spirit inspiring someone how to speak in certain situations. I don’t think of this as interior locution. This is just the indwelling of the Holy Spirit which we receive at Baptism and in which we are strengthened at Confirmation. When we live according to the Word of God and the teachings of His Church, we keep those lines of communication open. When we live in sin, we “clog the pipes,” so to speak.
With interior locution, the Lord speaks to one’s heart and soul, and the soul knows and understands Who is speaking for it knows the voice of its Maker.
***** Since we’re sharing experiences, I’d like to share one.
I have
always longed to have a relic of a piece of the Cross, but I never even prayed for one because I thought it was impossible. I thought only churches, or monasteries, or priests, etc., would have one, and who would give one up?? I never prayed about it because I figured why bother God with something impossible? It would be like asking God to have me sprout wings and fly!
Well, some years ago, I was on Main Street in Flushing, Queens, New York, early one Saturday morning. I had stopped to look into the window of a shoemaker’s shop who had some jewelry

confused

displayed in the window. On the only board I was interested in was 2 crosses in the top 2 corners, three medals below, and one cross below the medals. I had no plans to buy anything because I had only $42 to last all week (and it was Saturday), but was curious as to one of the medals - it was of a female Saint kneeling before the Blessed Mother who was holding the Baby Jesus. I was just curious as to which Saint it was, and not being able to figure it out, I turned to walk away.
As I turned, I heard (inside) as loudly and clearly as if someone had been on the sidewalk right next to me:
“GO BACK AND ASK.” I was so surprised, and thankfully all alone, I actually looked up and mouthed the word, “WHAT??”
Once again I heard:
“GO BACK AND ASK.”
Not wanting Him to have to tell me a third time, I turned and entered the shoemaker’s shop. The shoemaker greeted me and I asked to see the board with the crosses. At first, I looked at the medal, and then my eyes fell on the bottom cross. I saw the tiny pin on the bottom and knew it was a reliquary cross.
It was beautiful - sterling silver with intricate engraving. I was trying to figure out how, if I purchased it, would I live on $7 until the next payday, since the shoemaker wanted $35 for it. He wouldn’t let it out of his hands, and so I finally had to tell him, “Excuse me, sir, but I believe that if you turn the pin on the bottom, the cross will open.”
He looked at it closer and started turning the pin. As he did so, my heart started beating wildly even though my rational brain kept saying, “It’s probably empty, you know!”
When the shoemaker finally opened the cross, he squinted at it, then shrugged his shoulders and put it in my hand.
And there I stood, in a shoemaker’s shop on Main Street, Flushing, with a relic of the Holy Cross of Our Lord Jesus Christ in my unworthy hands.
No, it doesn’t have the papers, but it is sealed with the imprinted red wax and red threads, and I have absolutely no doubt that it is authentic.
I gladly paid the $35. (I told my landlord that I would be a week late with the rent that month.

)
When I walked out, it was as though I were in a trance, or in shock,
and what floored me the most was how He in his Goodness and Graciousness granted the desire of my heart even though I had never asked Him for it.
If this wasn’t a locution, then I don’t know what is.