Skype-to-Skype is free, Skype-to-Phone Line is reasonably cheap. There are other VOIP programs out there, too. But VOIP costs you in terms of data charges, so you have to be careful as to what kind of data plan you will have overseas.
Since the breakdown of long-distance phone service monopolies about 15 years ago, there are many smaller communication companies catering to specific long distance destinations. They have very affordable price plans. For example, I live in NYC, and call Russia all the time. I use one of these companies which cater to Eastern Europe and Former USSR. The way it works is similar to calling cards -- I dial a local American number, the computer tells me how much money I have on my account (you have to pre-pay) and then I punch in the destination number in Russia. My cell phone company (Verizon) counts this as a local call, and this long distance company charges me 2 cents per minute, which is very cheap, you have to agree! All my Russian destination numbers are programmed into my phone with a PAUSE in the middle, so I do not have to dial 24 digits every time, it only takes me two presses of a button -- first press for the local #, the second press for destination # in Russia. This connection process takes me probably only one second longer than the regular local call. The call quality is 100% perfect, I feel like I talk to people located in the other room. I heard of even cheaper plans, but every call there ether had a connection charge, or quality was not quite up to par, so I'm sticking with my 2 cents per minute, and I'm very happy.
Of course, what I just described concerns calls from the US to some other country, and you are interested in the opposite. But these same smaller communication companies offer very reasonable plans for calls in the other direction. It works the same way -- you pre-pay, and when you are overseas, you dial a given local number, and the computer connects you. So try to find these long distance companies, and inquire what price plans they have for calls into the US from your overseas destination. The company I use is Mastercall Communications, they have great deals for Russia, but I am not sure how they are with other countries, so they may not be the best deal for you. Shop around!