---
title: "Extension Guides"
slug: "extension-guides"
type: "index"
canonical: "docs.ucstack.io/extension-guides"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ucstack.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Cloud Extension Guides

3 articles

## [Reserved Extensions](https://docs.ucstack.io/docs/reserved-extensions.md)

Updated on 2025-07-23 | Published on 2025-07-11

The following extensions are not allowed to be used by any user . Additionally, Any number that starts with 9, and only contains 9's and 1's. For example: 9911 991 9111

## [Star Codes and Feature Extensions](https://docs.ucstack.io/docs/star-codes-and-feature-extensions.md)

Updated on 2026-01-13 | Published on 2025-07-11

## [Suggested Extension Ranges](https://docs.ucstack.io/docs/suggested-extension-ranges.md)

Updated on 2025-07-23 | Published on 2025-07-11

For Regular Users For System Extensions Session Initiation Protocol, a signaling protocol used for initiating, maintaining, and terminating real-time sessions that include voice, video, and messaging...