My bf played the guitar for our daughter and she loves music and dances all the time shes almost 3. She would move when I was pregnant with her so I think its effective. He is just starting to do it again now that im almost 24 weeks
I guess that depends on what you mean by "effective." I try to spend as much time as possible with music playing nearby. My son kicked and punched and did flips when I went out while pregnant to the club my husband DJs at, I always figured he liked it.
My son is smart but I don't attribute that to music playing in utero. He loves music and singing and playing instruments but he's heard it every day since he was born, not just in utero.
I don't know what you mean by "does it work" - it helps me to have music on, it keeps my stress level down, therefore it helps me. But the effect of music on a person can't be quantified. There's no "effectiveness" measure.
My husband says he study the difference in the type of music to play for a baby in the womb. He goes to the Pandora app and he only play classical music which is instrumental and he reads to our baby.