Q: Is it acceptable to call (phone) wedding invitees who have not responded via printed, stamped RSVP cards, to ask if they are coming?
A: Yes, it is. Call them, by all means. It is not at all rude to do so – the rudeness is on their part for not responding in time. You can be very upbeat and friendly – “just making final plans and hadn’t heard from you – we’re so hoping you can come to the wedding and I’m calling to see if you will be with us.”