There could be a number of reasons why you aren’t getting calls on your iPhone. The first thing to check is whether or not your iPhone is in airplane mode. You can check this by tapping on Settings and making sure Airplane Mode is turned off. If you still aren’t getting calls, check to make sure you are in an area that has service.
If your iPhone is not turned onto Airplane Mode and you know you are in a service area, call your carrier to see if there are any issues and that your iPhone is in fact activated.