Don't forget internet/e-mail. There have been plenty of times when phone calls were not possible due to downed long distance lines or busy switches but the internet will take a different route so if a circuit is down going from the eestern US to Europe then the route may have to to Europe via the Eastern US and take a little lobger but eventually get there. Vioce systems don't re-route like that.
HAM radio is also an option, even if you and your realtives don't have a HAM license and radio you may be able to contact an ARES (and whatever the Europe equiv. is) and have them relay a message for you.