The original iPhone, iPhone 3G and iPhone 3GS were only available on the AT&T network. AT&T is a GSM network, and only one of two such networks in the country -- the other being T-Mobile. If you purchase any of these earlier iPhone models and it's designed for a CDMA network, such as Verizon or Sprint, it's not an original iPhone. An iPhone 4 with a SIM card slot located on the right side is designed for GSM networks, while an iPhone 4 without a SIM card slot is designed for a CDMA network. The iPhone 4S and later models are designed for use on both types of networks. Any discrepancies between hardware and connectivity indicate that the iPhone is not original.