Is it a bad idea to have our 150 guests RSVP by phone instead of mail? My fiancé's extended family is not the most sophisticated, and I worry that they may not know to send back the response cards.

We recommend you stick with the mailed response cards. If yours were a small, informal wedding of 50 or so guests, RSVPs via phone or even email could work. But why would you want to be inundated with 150 phone calls so close to your wedding date? If you truly believe your fiancé’s family doesn’t understand the obligations implied by an RSVP (the abbreviation for the French réspondez s’il vous plaît, meaning “please reply”), start by plainly stating “please reply” instead of “RSVP.” Make sure to use reply cards with envelopes and stamp and address them (which is courteous anyway) to make it as easy as possible to reply. Then contact any stragglers by phone approximately two to three weeks before the date of the wedding. Ask family members and bridesmaids to help, if necessary.