Turn your iPhone into an iPod touch: No, your old iPhone won't make calls or hop on a cellular network without a data plan, but you can keep using it as a Wi-Fi only iOS device. To do so, you'll just need to keep the phone's old SIM card (or a cheap SIM card from the same service provide you originally used to activate the phone with) inside it. From there, you can restore it to factory settings, and set it up as a brand new device.