Why are prison phone rates so high? Experts say inmates are subject to monopolies and surcharges because they're unable to shop around for phone providers. Nationwide, the average cost of one 15-minute phone call from jail is $5.74, but that amount can range as high as $24.82, according to the Prison Policy Initiative. Those rates don't include additional fees, such as charges for setting up an account or listening to voicemails. Most people detained at county jails are typically held temporarily, often housing those awaiting trial or intake into the state system for longer sentences.