Cell phones reduce drama in a plot. If you let phones seep into the plot at all, you then have to bend over backwards to explain why one character can't simply call another at any time. A lot of shows pretend they don't exist.
But, but, but! Triangulation by infiltrated and gag-ordered by corrupted government carrier/ISP! End to end encryption! Trojans! Malware! Hacked Wi-Fi! Burner phones! Bought with anonymous and forbidden cash, or even stolen! War driving! The possibilities are endless!