old_contents: from django.contrib import admin
  
  from .models import VoiceCall
  
  
  class VoiceCallAdmin(admin.ModelAdmin):
      list_display = ['id', 'created_at', 'msisdn', 'duration', 'reason']
  
  admin.site.register(VoiceCall, VoiceCallAdmin)
  
new_contents: from django.contrib import admin
  
  from .models import VoiceCall
  
  
  class VoiceCallAdmin(admin.ModelAdmin):
      list_display = ['id', 'shortcode', 'created_at', 'msisdn', 'duration',
                      'reason']
  
  admin.site.register(VoiceCall, VoiceCallAdmin)
  
subject: add shortcode to admin