Can iMessages be sent internationally for free?

I was wondering if an iPhone in the US could send an iMessage (non-SMS/MMS) to another user's iPhone in another country (eg. Europe, South America, Australia) for free, even if one person has a US phone number and another person as a foreign phone number? In RCS messaging on Android phones, I don't think there is that capability or if there is it may incur a charge depending on the carrier.