Setting up new iPhone from old one and cellular service didn’t transfer

If that old phone uses the same size SIM as your new phone (which uses a nano SIM), then just pull that SIM out of the old phone and put it in your new phone. How your phone (any phone) connects to the cellular network and your account is controlled by the SIM, not iOS.

Gum4hawks wrote:

Why didn’t my cell service transfer to new iPhone

It's not part of the transfer, you need to activate your phone through your cellphone provider.