Will my IPhone 4S with Verizon work without the SIM card?

I lost my iPhone in a taxi, and luckily tracked it down with Find My iPhone the taxi driver had my phone turned off with the SIM card taken out but, my phone is working without it? I can make calls, and I have service. Everything on my phone is still there. What's the purpose of the SIM card if my phone is still working?

Maybe he changed the sim card? Because if there's no sim card you can't activate the phone.

A Verizon iPhone 4S is a 3G phone. Verizon's 3G works on CDMA technology which is not SIM based. The SIM card on a CDMA phone is for use if you travel globally.

Verizon is a CDMA carrier. They don't use SIM cards & as such work normal without them. Usually they issue SIM cards for international travel as GSM (the one that does) is the more internationally accepted format.