Elastix:

Elastix is a Distro with Asterisk 1.4.17 with lot of features

feature list
The features provided by Elastix are many and varied. Elastix integrates many software packages, each including their own set of great features. However, Elastix adds new interfaces for control and reporting of its own, to make it a complete package. Some of the features provided natively by Elastix are:
VIDEO support. You can use videophones with Elastix!
Virtualization support. You can run multiple Elastix virtual machines on the same box.
Really friendly Web user interface
"Fax to email" for incoming faxes. Also, you can send any digital document to a fax number through a virtual printer.
Billing interface
Module for automatic outgoing campaigns
Graphical configuration of network parameters
Resource usage reporting
Remote restart/shutdown options
Incoming/outgoing calls and channel usage reports
Integrated voicemail module
Voicemail Web interface
Integrated operator panel module
Extra SugarCRM and Calling Card modules included
Download section with commonly used accesories
Embedded help interface
Instant messaging server (Openfire) integrated
Multi-lingual support. Languages supported include:
English
Spanish
Rusian
Korean
Greek
Chinese
Polish
German
Frensh
Romanian
Slovenian
Portuguese
Danish
Italian
Mail server integrated including multi-domain support
Web based email interface

A fabulous appliance: PEPLINK LOAD BALANCE 200/300

PePLink offers the only affordable link load balancers (dual-WAN and multi-WAN routers) with advanced, enterprise-grade features.

Features Benefits

Link Aggregation & Load Balance Faster, more reliable Internet made easy.
Drop-in Mode Easy, transparent installation
Integrated DNS Support of NS, A, MX, CNAME and TXT records
VoIP, SIP, and Vonage® Support Fully compatible with major SIP-based VoIP
providers. Enjoy your calls.
QoS for VoIP Better and clearer sound quality for your voice calls. Session Binding Compatible with secure web, e-banking, and other
applications.
Inbound Load Balancing Optimal use of two or more WAN links for incoming
requests to your servers.
Hardware High Availability Utmost service protection by deploying two
PePLink Balance devices side-by-side with VRRP

AVAYA IP500: New generation of PABX by AVAYA

IP500 is the next generation of the IP Office, designed to meet the needs of small to medium sized businesses. Supporting a range of trunk configurations, including SIP, IP500 will scale from 2 to 272 users. IP500 supports IP Office v4 software, offers a range of voice and data features and is well suited to installations of an IP-Centric nature. Due to its modular design, the solution can scale from 2 to 360 extensions to meet the needs of home offices, standalone businesses, networked branches and head offices. Built on Avaya's latest advancements in converged voice and data technology, small to mid-sized businesses can benefit from many of the advantages sophisticated communications deliver to their operations.

Microsoft Office Comm Server: feature glut, proprietary, pricey, and too Enterprise-centric by ZDNet's Russell Shaw -- During "Unified Communications Day" in San Francisco, Microsoft announced that a new Office Communications Server 2007 would bundle voice (including presence-based VoIP call management), video, IM and email into a single enterprise applications platform. Additionally, Office Communications Server 2007 will contain the Microsoft Office Communicator 2007 client -which will in turn, offer a VoIP softphone. Pardon me [...]

Abstract in English of my work placement project:

Optimization and Security of a interconnection platform

The goal of this project is to build a SIP routing plate-form, to secure it and to provide the best of Services Quality.
This platform has to receive and manage SIP calls (SIP is one of most important VoIP protocol allowing voice, video and data transfer over Internet network) and route these calls toward different gateways. Asterisk system has been selected as the main core of this routing platform.
VoIP traffic will cross over public Internet network; the major issue is to choose a safety policy. To do this, we have decided to use one of partner’s products of Questo: SIP Firewall SIPAssure from the Canadian firm Borderware.
One of our goals is to have a good quality of service for our future users. Then, we decided to use a QoS product with load balancing, prioritization and aDSL link aggregation functionalities. This product is PePLink Balance 200, from one of Questo’s partners.
A phase of tests allows to validate previous both points. The purpose is to see the effects of two threats taken in example, the DoS attack (denial of service) and the attack by impersonation on the infrastructure, unprotected time and the other time with protection.

Since a long time, Phone is one of main tools using by all firms in the world. This last years, with the Growth of the IT networks, telephony become including on it with the name VoIP (Voice over IP). Contrary to Public Switched Telephone Networks (PSTN), like France Telecom phone network, with private central plateforms, VoIP allows a real time transport of voice in all of analogic and numeric networks thanks to TCP/IP protocol (procol for Internet).
VoIP opens new developpement for voice and data transport. That's why, actually, we spoke about convergence between Voice and Data
This convergence simply network and telecom administration and developpement of voice and data software.
We can imagine easier all possibilities offered by a voice and data CRM application.

Second interesting thing, offered by VoIP, is economic. Lot of companies loose lot of money in phone billing (for internal call or long distance call). A price of an Internet call is ridiculous if we compare with price of a PSTN operator's call)