The quotes below pretty much sum up the reasons the MOB is entertaining a phone ban:
Really, I think people place way, way too much importance on their "need" for their cell phones and not enough on real human interactions. No one should have to be told to not use a cell phone at a social event; they should know it to begin with. But, since they don't, I don't see any reason that the word shouldn't be put out that the wedding and reception are a cell-phone free event and that no photos be taken by guests. If one must have a picture of great-aunt Marjorie, then I see no reason why they cannot wait until afterward (or before) to do it. They don't need to take the picture during the actual event. It's just not that difficult.
I think expecting no pictures are taken even during the reception is deluded. If you ban cell phones, people will bring regular cameras.
It's totally fine to ask no pictures being taken during the ceremony (we had it in the program and the clergy-person announced it at the beginning of the service to please only take pictures during the processional, the recessional and right after we exchange rings. Yes, we paid a professional photographer to pretty much just hang out during a two hour catholic bridal mass.
But I really think you can't expect people to not take any pictures during the reception. People took pictures during weddings well before the advent of cell phones. And they might want to have some pictures even of the bride and groom to remember the event. Or will the bride and groom give pictures of themselves from the wedding to all wedding guests?
When my cousin got married my husband (then fiance) snapped a picture of myself with the bride and groom. Only people who have seen my photo album (pre-digital) have seen the picture, but it is a great way for me to remember the event.