I have lost my iPhone and have locked it, I've been using find my.. to locate it. The location is updating but all my calls are going straight to voicemail, what does this mean?

I am assuming that the cellular service is still active on your locked iPhone. You have been calling the lost iPhone and your calls go straight to voicemail. This happens when an iPhone has been turned OFF, or iPhone has poor or no service in the area or the battery of the iPhone is dead.

Also, please review this guide published by Apple 👉  If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support.

Axel F.