Many wedding invitations use the traditional method of giving a printed card, rather than supplying an email address or phone number to contact them on, as it is more formal and weddings carry a lot of formalities.
If you are on budget, the mot inexpensive way is to provide a email address and / or phone number underneath the invitation details.
Both types of RSVP’s, use the same stock as the wedding invitation, so that all stationery is matching. The difference with the cards, is, the card and envelope, the RSVP details are hidden, but this option is slightly more expensive then the postcard style.
The RSVP cards are generally a plain card with no embellishments, such as ribbon, lace or diamantes. This is because they are returned to the invitee and are usually not kept after the wedding.