Sprint To Unlock Its Phones, Allow Non-Sprint Phones

Sprint unlocks their phones, but other carriers aren't obligated to activate those phones. I thought Verizon specifically didn't activate esn's not in their database (to maintain network quality by only having authorized devices or some crap like that). And they say they'll allow other carriers devices on their network, but don't they also need to be unlocked?

To be honest, I didn't even know CDMA phones were actually locked. I thought the carriers controlled device access by allowing or disallowing esn's on their network.