I just activated a galaxys5 but when I make a call I get a message that says Verizon is unable to authenticate my phone.
You need to call Verizon at 1800-922-0204, and discuss troubleshooting with them. It sounds like the SIM card got activated, but not the ICCID of the device. I'd try restarting the phone as a last resort before you call though, because wait times can be long.
did you complete the activation process??
