Unlocking an iPhone for free with an IMEI number is only possible if your carrier offers free unlocking. You can contact your carrier, provide the IMEI (found under Settings > General > About), and request an unlock—if your phone is eligible (e.g., fully paid off, not reported lost). Avoid websites claiming to unlock for free with IMEI, as many are scams. Apple itself does not unlock iPhones; it must go through the carrier.