You do if you are opening an account with one of those carriers for the first time. Verizon and Sprint won't just sell you a SIM card unless they can add an IMEI to their database. It's a relic of the CDMA days that is no longer technically necessary, but they do it, anyway.You don't even need to "activate" it with the carrier, just get a sim card and put it in, restart phone. Its that simple.