Check the eligibility first, use the following service under CHEKMEND / IMEI / ESN CHECK section:
Sprint USA - iPhone Eligibility Test (Clean/Blacklist/Unpaid Bill)
This service is active on business days only. No processing on weekends/Holidays.
IMEIs starting with 99** are NOT supported.
iPhone 4, 4S and iPhone 5 are NOT supported.
IMEIs that can NOT be unlocked will be rejected and refunded.
iPhone 5C/5S/6/6+/SE/6S/6 Plus/7/7+ are supported.
Clean, out-of-contract IMEIs only!
Phone MUST be previoulsy activated and have a clean IMEI for best successs rate.
Brand new and never activated phones aren't supported.
*** NO REFUND FOR WRONG IMEI, NON-SPRINT IMEI AND ALREADY UNLOCKED IMEI. ***
If your Sprint iPhone is blacklisted, has unpaid balance or being financed
it will likely be rejected by this service and will be refunded.