Is there any way I can activate my iPhone 4s with a SIM card different from the carrier?

Is there any way I can activate my iPhone 4s with a SIM card different from the carrier?

Only if your phone is unlcoked

Jailbreak

You can only do that if the iPhone is unlocked. If it isn't, then you have to use a SIM card from the carrier that it is locked to. I know, it sucks, but that's just the way Apple does things.

What I recommend is to call the carrier it is locked to and ask if they can unlock it. Usually they will, as long as no money is owed or not reported as lost or stolen.

Your current carrier would have to unlock the phone for you. The SIM card would only work if your new carrier uses the same technology (GSM or CDMA) as the old carrier.