Aren't cellphones irritating enough in life? Don't we have to deal with enough of this shit when we're conscious? Don't get me wrong, I'm all for burying and burning cellular phones, just not alongside people. Do you really think you're going to pick up the phone post-postmortem and, getting a perfect 5 bars of reception, just dial up a buddy. "Yeah, Merle, I'm dead. No really. So, how's Tina?"
That being said, death is a very personal thing so I think anyone who really wants to be buried with their cellphone should, of course, have their request met. Preferably sooner than later.