I have upgraded to an iPhone 5S, and I already wiped my iPhone 4S and taken out the SIM. Now my mom asked if she could play with the 4S. I turned on the 4S and it insists on having a SIM so it can be activated. What happens if I put the old SIM back in? Will the phone activate and I'll suddenly have another 2-year phone service contract on my hands? Is it possible to use the old 4S as an iPod Touch without any phone service?