Since we had decided to do a paperless RSVP, and we're expecting guests over the age of 50, we thought it would be best to provide our invitees with a phone number they could use to respond. It could be a little awkward, though, if one or both of us had to deal with fielding calls from friends and family while we were working or otherwise unavailable, and with our international relatives the timing could have been a problem. One option would have been a paid RSVP phone service like these guys, but why pay for something we could set up ourselves for free?
Instead I requested a Google Voice invite from a friend (of course, not long afterwards they opened up the service to everyone), and set up a new account using our shared email address. We chose a phone number (nothing good available with 10/10 in it, unfortunately), recorded a message in about half a dozen takes, and we were done. We used Ellie's phone number to link the account to, but turned off call forwarding in the settings, so all calls go directly to voicemail. We both get an email alerting us when a new message comes in (with an attempted transcription, but so far Google's servers have trouble with English accents), and one of us just pulls up our RSVP web page (detailed post on that coming soon!) and submits a response for the record. As a bonus, Google stores all the voicemails - no worries about running out of space - so we can always go back and check if we think we could have written one of them down wrong.