ATT Data Plan use in unlocked cell?

So I purchased an ATT Data plan with the sierra mercury usb stick. I was wondering if I purchased an unlocked phone and stuck the data plan SIM in in would it work? I see on my monthly bill that I have caller id, 3 way calling, call forwarding etc....all the phone stuff. So....can i pop it in a phone and use it?

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There is no included voice time with the plan. You would pay $0.40 per minute for voice calls.

VOICE CALLING: If you have a voice-capable device (unless you request voice blocking, select a data plan that restricts voice access or select a qualified voice plan), the default rate for voice calls on AT&T’s wireless network is $0.40 per minute and $0.69 per minute for domestic roaming voice calls off AT&T’s wireless network. See AT&T Nation map for default voice coverage area.