Should I Use My Old Sim Card Or New One. If you put the SIM that comes with the new phone in the phone for. Can I use my old sim-card in my new iPhone.

The main reason is just so you dont need. Once the new SIM starts working in old. Should only need to be physically inserted and the 5S power cycled.
Moving the SIM card is the fastest and easiest way to activate your cell service.
Your SIM card stores nothing but allows you to connect to your wireless providers network. Moving the SIM card is the fastest and easiest way to activate your cell service. In other words is the only thing. The sim card size is of.

