So as soon as I say that they don't use cell phones on Buffy, out comes a cell phone.
More Buffy stuffy: It's nice to see someone with a big budget make the kinds of mistakes which we tend not to make. We would have painted this boom mic out (I think this was a static shot so it's fairly easy to do.) It may have been that the boom went unseen on the broadcast version because it was beyond where most TV's have image. Still, it amuses me.
Remember back in the olden days when mics would creep into frame in movies in the theater? I think that's because movie theaters were much worse about having correctly calibrated projectors and they showed you more frame than they were supposed to.