Not being a member of the latter category I was always going to need something more than the situation itself to maintain the suspense. The director clearly gave some thought to this (hence the snake interlude for the alternatively phobic) but the deployment of the chosen ideas is somewhat haphazard.
I suppose one can also enjoy the film as a dark satire on the American way of telephony with particular emphasis on customer and employee relations.
The trouble is that all this focus on the cellphone and the strange and pointed conversations that it faciliates with the world outside and above the casket, ultimately detracts from the verisimilitude of the scenario. Grade: B (+-)
* I suppose this deserves some credit as one of the few modern horror movies where mobile phones don't require plot-excision and where the audience isn't treated to the seemingly obligatory 'no signal' shot!