Good news. The service works the same way for state prison as it does for county jail.
Here is how it works. Every facility uses a phone carrier, and that carrier sets rates based on the phone number being called. Those rates vary depending on the number's area code, carrier, and location. InmateAid's system runs your number through an algorithm that checks the carrier's own rate calculator and determines whether a different forwarding number can connect you to your inmate at a lower rate than what you are currently paying.
If a savings opportunity exists, InmateAid assigns you a number that routes calls directly to your cell phone at the lowest published rate available. From your inmate's perspective nothing changes. He dials a number and reaches you. On your end the call forwards seamlessly to wherever you are.
The rates differ from facility to facility and carrier to carrier, which is why the algorithm matters. What saves someone 80% at one county jail might save a different amount at a state prison, but the system accounts for that automatically.
If you signed up under the assumption it was county jail only, your account should work as is. The underlying mechanism does not distinguish between facility types, it just finds the best available rate for your specific number and location.