I spent over an hour trying to figure out how to insert my micro SIM card into the open slot in my new PinePhone, before realizing that the procedure simply requires removal of the battery. To avoid frustrating new buyers I would add this simple little tip to the written instructions shown on the pine64.org wiki.
The PinePhone’s SIM slot requires a micro SIM, please do not insert a nano SIM without an adapter. An adapter from a nano to a micro SIM might be included under orange tape in the camera notch of the phone’s packaging. The SIM card has to be placed in the lower slot, while the microSD has to be placed in the upper slot, as pictured here: