curl --request GET \
  --url https://api.topcalls.ai/v1/phone-numbers/carriers \
  --header 'Authorization: Bearer <token>'

{
  "carriers": [
    {
      "voip_carrier_sid": "660e8400-e29b-41d4-a716-446655440001",
      "carrier_name": "My Custom Carrier",
      "is_default": false,
      "is_system": false,
      "trunk_type": "static_ip"
    }
  ],
  "default_voip_carrier_sid": "550e8400-e29b-41d4-a716-446655440000",
  "count": 1
}