curl -X DELETE "https://api.telzino.com/v1/organizations/234cd323-…/sms-numbers/%2B13234137301" \
  -H "Authorization: Bearer YOUR_ACCESS_TOKEN"

{ "data": { "phone_number": "+13234137301" } }

{
  "error": "number_in_use",
  "error_description": "That number is in use. Take it off these agents first.",
  "in_use_by": [
    { "type": "conversation_channel", "agent_id": "9f1c…", "agent_name": "Front Desk" },
    { "type": "send_hosted_sms", "agent_id": "71f7…", "agent_name": "Sales" }
  ]
}