Your iPhone calls going straight to voicemail in iOS 18 could be due to a simple setting or a technical issue. First, check if Do Not Disturb or Focus Mode is enabled under Settings → Focus and turn it off if needed. Also, ensure Airplane Mode is off, as it disconnects your phone from the network. Poor signal or Call Forwarding being enabled can also cause this issue, so check your network and disable forwarding under Settings → Phone. Additionally, blocked numbers may be preventing calls, so go to Settings → Phone → Blocked Contacts to review and unblock any numbers. If unknown callers are being sent to voicemail, turn off Silence Unknown Callers under Settings → Phone. Some third-party call blocking apps might also interfere, so try disabling them. Updating your carrier settings in Settings → General → About and restarting your phone can help fix minor glitches. If the issue persists, contact your network provider for assistance.