How else would you make and receive phone calls then?
edit: i totally didnt know gsm and 3g were different (communication) technologies ignore my statement 🙂
I thought 3g data and voice went hand and hand with gsm.
For whatever reason, in my experience, I'd only hear the buzz on nearby speakers (and speakerphones or landline telephones or clock radios) when the iPhone was accessing data (email, internet, whatever.) The GSM buzz wasn't present when I was using it to just make calls.