We definitely use more data with 3 iphones on my family plan. As for voice, we hardly use our 700 minutes we get each month. I think I used 87 minutes of peak (non-mobile to mobile) minutes last month. I'm not a big talker.

With this talk of Verizon and AT&T getting that unlimited voice and data plan where you can share data between (upto) 10 devices. It sounds like a good plan but it's not practical for us since we don't use a lot of minutes.