Talking through the car stereo

[Butokan]

I was listening to music from my phone in my car through a cassette adapter. I got a call from my daughter. I answered and she said "hello". I responded with a "hello" thinking she wouldn't hear me. To my suprise she did. I didn't know that if you had something plugged into the headphone jack that didn't have a mic, the phone would use the buolt-in mic. I wonder if this would be the case with headphones without mics. I can't test this out, because I don't have a pair of headphones without a mic.