If the prisoners were able to keep the “no longer useful/update-able” device but the content is revoked, then they are back to buying pre-recorded audio cassettes (which is a surprisingly thriving market), then I can see the EULA applying. The EULA would need to meet the standards outlined in Fitness For Purpose. This would be a hindrance to future sales if this behavior continues.
This assumes that the devices are capable of being operated in a stand-alone mode with no network connections.
Since the legacy devices are (assumed to be) being taken away (assuming that the hardware was a one-time “purchase”, I would submit that doctrine of first sale applies as 1) device was “sold” (or sale facilitated) to the prisoner by the prison itself and 2) the device is considered “frozen in time” in the present state once the “music stops” on support/updates (sorry, bad pun), and the combination of hardware/software is then treated as piece of fixed media collection.
