Hey innerscorecard- I don't live abroad, but I travel several months a year and have a couple insights for you.
-All of my services work fine, but when I move around to different countries, I often need to answer security questions again to reestablish my identity.
-Google Voice (plus Groove IP and Ring.TO if you have Android) is your friend! If you don't already have Google voice, log into your Google account and make sure it's set to American English. Then you should be able to setup a Google voice number for free. You might also need to use a US proxy. Once you have a Google voice number, you can make and receive calls from your computer to the US, anywhere in the world that you have an internet connection, for free!
-Take Google voice one step further if you have Android by using the app Groove IP, which will allow you to do the same thing from your phone, with a different phone number (provided free by Ring.TO). I recommend making your Google voice forward to your Ring.TO number. This way you can give people your Google voice number and still receive calls both on your phone and computer. In my limited experience, Google voice is more reliable than Ring.TO.
I can't imagine you'd have any unsolvable problems if you just explain your situation. If you have a US mailing address and phone number, you shouldn't even have to explain your situation. I was able to open my vanguard account while traveling with no problems that couldn't be solved by a quick call to support.
I hope this helps!