You need a sim to activate the phone. There is no way around this.
While the phone can function without a sim card once its been activated, activation requires a sim card. If the phone is locked to particular carrier, the sim card will need to be from that carrier. Otherwise it can be a sim card from any carrier.
The sim card however does not have to have active cellular service on it, but does need to be working. You can borrow a sim card from someone just for activation. Once activation is complete the sim card can be removed.
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