And never in a billion years would I stuff a paper wedding invitation into a regular business envelope and scrawl a name and address onto it...
... and I certainly wouldn't have people RSVP via a text message or email.
Come on! It's your wedding, people! The fact that this invitation has "six o'clock in the evening" spelled out tells me they were trying to be a little bit formal about it, but with the text message thing it sends a mixed message.
And then can we go back to the envelope for a minute? The guests' last name was just scrawled on it. Not Mr. & Mrs. Jones, but Jones. Not The Jones Family, but Jones. Is it a shotgun wedding? Is it an arranged marriage? Where's the joy and celebration...? I don't know about you, but I've gotten mail addressed to Occupant that seemed a little more cheerful than that. oy.
Do it all on paper or do it all online... just do it consistently. And try to show just s smidge of enthusiasm, mKay?