CDMA

Code Division Multiple Access MNO networks were an alternative to GSM that were used for some networks around the world, the most well know being Verizon and Sprint in the US. CDMA did not use the SIM as the subscriber identity and never evolved beyond 3G and so all 4G and 5G networks are now GSM. With no SIM in theory CDMA was harder than GSM to create an MVNO, however Sprint had numerous MVNOs nonetheless.