That won't work because someone could slip an i4 back onto it although he'd have to cut the tabs off the inside. Siri should be in settings as well. Be wary if it's jaiilbroken as Siri could be added to iPhone 4 that way.The model number printed on the back of the GSM-equipped iPhone 4 is A1332, the model number on the back of the CDMA-equipped iPhone 4 is A1349, and the model number on the back of the iPhone 4S is A1387.
I think he's referring to how the CDMA iPhone 4 has no sim card. so if the OP looks at it and it doesn't have a SIM tray then it is definitely a 4, if it does have the sim tray you have to look at other things since it could still be a GSM 4. Probably the easiest way is checking to make sure it isn't jailbroken and that it has Siri.Your iPhone 4 SIM tray slot is on the left