Video messages from guests

I am interested in having our guests each leave us a personal message on our wedding day. I don’t think our videographer will go person to person (I will ask), and we don’t have a video booth option, so I’m considering using an app people will download to their phones (unsure if people will actually do this?) or having my sister use just an iPhone and go around asking if people would like to leave us a message. Have any of you done the photo app option or going around with an iPhone option? I’m open to all suggestions.