If it's a CDMA phone without a SIM card, it can't be SIM-locked (which is what "locked" really means) so it can't be unlocked. All unlocking does is allow the phone to use SIM cards from other carriers.
Since your phone is a Sprint phone, and the only other CDMA carrier in the US is Verizon - and they won't accept Sprint phones on their network - the only other networks you could use would be MVNOs that use Sprint's towers - like Boost. And whether you can or not is up to Sprint.