HTC One M8 User Manual page 22

22 Unboxing
nano SIM card
HTC One uses a nano SIM card.
Use a standard nano SIM card only. Inserting a modified card that is thicker
than the standard nano SIM card may cause the card to not fit properly or
damage the card slot.
Inserting a nano SIM card
1. Hold the phone face up.
2. Insert the tip of the tray eject tool (or a small bent paperclip) into
the tray eject hole next to the nano SIM card slot.