Not permissible on Sprint.
Taken from the Terms and Conditions of their "Everything" plans:
"Except with Phone-as-Modem plans, you may not use a phone (including a Bluetooth phone) as a modem in connection with a computer, PDA, or similar device. We reserve the right to deny or terminate service without notice for any misuse or any use that adversely affects network performance."
You need the add-on, or they can terminate your service.