How much does it cost to use opera mini on the upstagge phone to use with sprint?

If you have unlimited internet with sprint does it still cost money to get on opera mini or does opera mini work as if i have unlimited internet on it too. So if i have unlimited internet on my phone would it have unlimited internet on the opera mini also i have a Samsun upstage phone from sprint.|||Opera mini is still free. Only Opera Mobile, the version for PDAs and PDA phones, costs money.