There were no activation for GSM phones. You insert a whitelisted SIM and the phone would just register(login) to the network. The network doesn't care. Phone might care, but it's processed instantly on the modem. It was Apple that added online "activation" gimmick to it.

"CDMA" networks built on proprietary Qualcomm cdma2000 standards used its equivalent of eSIM, and that was why it required special trusted phones for OTA programming. It was also used by Verizon which IIUC had better coverage than others so lots of people would have had memories of having to go through something akin to Apple activation.