Most mobile plans these days let you call just anywhere in your home country without incurring extra fees, and a few even have some international calling included. Phoning Europe from the US is usually spendy, though. For the next few days, a couple carriers have waved all fees associated with calls or texts from the US to Belgium in the wake of Tuesday's terrorist attacks.
We're not going to get into the specifics of what happened—there are news outlets that specialize in reporting on heavy issues like that (see BBC and The Guardian for coverage). We write about phones and stuff. The relevant bit here is that both Verizon and AT&T have decided to offer free calls and texts from the US to Belgium so you can contact friends and family.
Verizon won't charge for calls and texts made on March 22nd (today) or 23rd. AT&T is crediting all charges for calls and texts to Belgium from today until March 28th (Monday). Calls on Verizon and AT&T's wireline service are included too. T-Mobile and Sprint have yet to announce similar measures, but it's common for all the big carriers to match each other at times like this. We'll update if there's news.
Sprint too. No fees through March 31st, and it applies to Virgin and Boost as well.
T-Mobile has followed the others in offering free calls and texts to Belguim. It runs from today until March 25th (Friday). Both Tmo and Verizon had free calls and texts to Turkey, but for Tmo that ended on the 22nd and for Verizon was over on the 20th.