So, I have been trying for two days to activate. When I click cellular it says ATT loading plan then goes back to Set Up Cellular. When I click on that, I continue to get get Oops something went wrong EDS0241.
I totally feel your frustration, it is completely on AT&T side but being new technology I think they are figuring out how. Do you have WiFi calling feature turned on? If not can you turn that on? Also, do you happen to have a another AT&T SIM card by chance for your iPhone?