Shortly after ISIS-affiliated gunmen killed over a hundred people in multiple attacks in Paris on Friday evening, Google allowed users of its Hangouts chat platform to make free VOIP calls to France from anywhere. Later this weekend American telecom companies have followed suit. Carriers Verizon, T-Mobile, and Sprint are allowing their customers to call French telephone numbers without incurring international calling charges, and Skype is allowing free SkypeOut (VOIP-to-standard phone number) calls into France.
Verizon is allowing free cell and home calls plus free text messages this weekend. Sprint is offering free calls and texts to France for all customers, prepaid and postpaid, with no end date at the moment. (That also applies to Sprint subsidiaries Virgin Mobile and Boost Mobile.) T-Mobile is offering free calls to postpaid customers only through Monday (tomorrow) in the US and Puerto Rico, though the press release notes that customers will see both charges and rebates on their bills.
Skype users all over the world get free calls to landline and mobile phones in France for "the next few days." At the time of writing, AT&T is the only carrier among the US "Big Four" not to offer free calls to France following the attacks.
A few hours after posting this story, an AT&T newsroom post stated that the company would be crediting (refunding) all call charges made for calls to France between November 13th and 17th (Tuesday). This applies to both wireless and landline accounts. Customers who've already made calls to France should see the credits applied on their next bill.