As with most things, follow the money. Without cell phones, the only way that a prisoner may communicate with loved ones outside is through collect phone calls. These collect phone calls are outrageously expensive--about $20 for 10 minutes. The reason is that the prisons sign exclusive contracts with phone providers and get a cut. It's wrong on a number of levels:
1) Usually the families of prisoners can ill afford such rates.
2) Families make reasonable economic choices to limit the calls that they take. This further isolates the prisoner from his family (and support system).
3) We all know that legitimate companies are able to make money charging only 2 or 3 cents per minute on long distance calls. The 10,000% mark up is unconscionable.
These anti-cell phone policies are really just an attempt to protect a lucrative revenue stream.