Noted that you won't have your notebook with you all the time but on those occasions that you do, you might consider buying a Majicjack before leaving the US. It's a little widget that gives you a VOIP connection via broadband. One end plugs into the USB port, the other is a standard RJ11 connection where you plug in your phone (I presume the softphone will work with the microphone and speakers in your notebook). Why Majicjack? Because the widget is $40 (includes first year of service, second year on $20/year), calls to the US and Canada are free and the sound quality is like calling across the street on a landline. And you have a US number - you can choose an Alabama area code. Your friends can call you when you're on line, and it would be a local call for them.
I use mine from Singapore. But before you buy, be aware there are as many people that hate it as love it. I guess when it works it's great but when it goes bad then customer service is nonexistent. Others have written about this on FT, try searching the threads.
For other times, you can do as christep suggests, use a calling card and call from payphones or other people's phones.