It LOOKS like a US phone number. You DIAL it like a US phone number. But, you are NOT charged like a US phone number. I highly recommend using a landline and/or calling cards, as international calls from a cell phone are RIDICULOUSLY expensive. For me, INCOMING calls are FREE (yay! call as much as you want, as long as I have reception and power on my phone!). Outgoing calls to the States are 17 cents/minute, which is pretty expensive, but worth it every once in a while.
I do NOT have voicemail, even though it will go to voicemail if I don't answer. I will NOT get voicemail messages. Where they go... I have NO idea. If I don't answer, just try back another time. Reception in my village can be shady. If I see you calling, I will be sure to pick up! :)