Unlock sim after passing opportunity to unlock on iPhone startup

This must be some basic stuff but I'm unable to figure it out. I've restarted my iPhone, inserted my security code and then when the numpad appeared to insert my SIM pin code, I pressed the home button and now I can't trigger that numpad again to insert my pin code. The only thing I see is Locked SIM in the upper left corner and can't do anything about it. The question: How can I trigger the panel to unlock my SIM card again?