There are many magazines either focused directly on VOIP or that are useful for information about related topics such as networking, telephone systems, etc.

www.voip-info.org is happy to make available totally free subscriptions to many technical magazines. The only catch is that you must be a qualified industry professional. i.e. there is some chance that you might be a buyer for or influence the purchase of the products and services advertised in these magazines. Each magazine usually has a short qualification form to fill out.

I have subscribed to many of these magazines for years and found them very useful.

• Free Technical Magazines

Should you have any problems with this service, please let me know.

Thanks
support@voip-info.org

Examples of Magzines available:

• Packet Magazine - Provides the latest on Cisco technologies and products, including tech tips, configurations, and links to online resources...
• Total Telecom - "The Economist of the communications industry"
• Communications News - Serves the decision makers responsible for networking, voice data, and video communications technologies at enterprise and service provider organizations, both in print and online...
• RCR Wireless News - Is the only weekly newspaper covering wireless, has met this challenge, offering a mix of breaking news and in-depth analysis into the issues that mold today's wireless telecommunications environment....
• Network Computing - Provides labed solutions for your toughest enterprise-wide computing challenges.
• Oracle Magazine Contains technology strategy articles, sample code, tips, Oracle and partner news, how to articles for developers and DBAs, and more
• xchange - Covers revenue-generating service-delivery strategies for full-service facilities-based providers — from incumbents to competitors — serving metro and rural residential and business communities.
• Many more

Examples of Whitepapers available:

• Best Practices for VoIP Security - Defines industry best practices for Enterprises to secure both enterprise networks and the voice traffic riding on these networks....
• Defending eBusinesses and Hosting Service Providers from DDOS Attacks - Discusses defenses required for Service Providers and ebusinesses to protect their servers from such attacks....
• 90 Page IP Telephony Pocket Guide - Describes the issues decision makers will need to understand as they set out to build a winning IP business communications strategy...
• Customers Rate IP Telephony Systems - This independent report (not sponsored by ShoreTel) includes a comparative assessment of the top IP telephony vendors.
• FierceVOIP - Is a free twice-weekly email service for elite executives in the voice over IP and IP telephony market...
• VOIP Security for Telecom OEMs - How to build robust security into carrier-grade devices Discuss how to ensure the security and availability of new services such as VOIP over Unlicensed Mobile Access (UMA) and IP Multimedia Subsystem (IMS) architectures...
• Many more

Thoses ones are free and very interresting

• http://emags.tmcnet.com/emags/latest-issues.aspx/

This resource is public and interesting for voip comunity:

• http://voip-in.net/