Can't make any phone calls. . .

I'm new to smartphones, so please bear that in mind. Among the host of issues I'm having trying to get my newly purchased SE iphone to function is its failure to make phone calls. I hazard to suggest that it can't be due to a problem with the sim card because I can access my Chrome emails. The persistent "No service" message at the top of the screen indicates deeper problems, on the other hand.

There many, many other issues at present, but I'll stick with the phone's inability to make or accept telephone calls, which is pretty fundamental, I guess.

Thanks for reading this post.