Remember my post on technology in Vampire and horror in general?
Is technology in Modern Day settings interfering with story? asks Labmonkey-XL on ye RPGnet.
And I say:
It depends. The “my phone isn’t getting any reception!” scene is so ubiquitous in horror and thrillers because they rely on isolation and uncertainty. It’s become a groan-inducing trope of those genres, and we've seen a rise in period genre pieces set in the 70s and 80s as one way of getting around it, but varying the reasons it won’t work, or won’t work well, can go a long way to help. As well as the various real-world options suggested above, consider a setting where magical or psychic powers can work over the phone or online. The Ring is essentially an update of Casting The Runes with a video instead of a scrap of paper, and its most recent sequel puts the video on YouTube.
I also discussed this here yesterday, as part of general GM advice for modern games in particular.