Is Microsoft ISA server supported as a firewall?

The issues with Microsoft ISA server 2004 and 2006

Unlike most professional firewalls, Microsoft ISA server is not able to do static port mapping. Without static port mapping it is not possible to reliably connect to a VOIP provider or remote extensions. This is not a 3CX issue but an ISA server issue.

The best solution is to buy a proper firewall such as from Linksys, Cisco, Netgear and others. Even a $100 Linksys router can do static port mapping. Configuration guides can be found here:

http://www.3cx.com/support/linksys-configuration.html

http://www.3cx.com/support/cisco-configuration.html

Microsoft ISA server is known to cause issues with other IP telephony systems. Please review the links below to confirm:

http://help.fonality.com/index.php/PBXtra_Installation_Guide#Warnings_about_Firewalls

http://help.trixbox.com/index.php/Trixbox_Pro_Installation_Guide#Warnings_about_Firewalls

http://www.voip-info.org/wiki-Asterisk+firewall+rules

General 3CX Phone System FAQs 

• How do I disable the dual Ring Tone?
• Can hotels with Micros Fidelio use 3CX Phone System?
• How can I translate the Prompt Sets?
• What phones, gateways and firmware have you tested 3CX Phone System V5.1 with?
• How can I setup integration between 3CX and Salesforce.com?
• How can I view SIP traffic with a Network Capture tool?
• How do I configure a CISCO router for to allow connection to a VOIP provider?
• Why does 3CX require static port mappings (Full Cone NAT)?
• What operating systems does 3CX Phone System support?
• How can I use the 3CX Tunnel with a SIP hardphone?
• How do I configure my Linksys router for 3CX Phone System?
• How to use fax if using multiple network interfaces
• How can I localize 3CX Phone System?
• How does Phone provisioning work?
• How do I create a phone provisioning template?
• How does 3CX Phone System decide whether a call is internal or external?
• What is the firewall checker and why do i need it?
• What is the cause of Installer error 2738, when installing 3CX?
• How to solve Source identification errors
• What is a SIP domain and how do I configure it correctly?
• How can I launch a call from a web based CRM package?
• How does 3CX know its an external extension?
• Does 3CX Support SIP trunking/ SIP trunks?
• 3CX Phone System Commercial & Free editions support page
• How can I adjust the configuration for unsupported VOIP providers or gateways?
• How do I configure direct SIP Calls?
• Configuring Exchange Server 2007 Unified messaging with 3CX Phone System
• What SIP Phones can I use with 3CX Phone System?
• What VOIP Gateways can I use with 3CX Phone System?
• Does 3CX VOIP Phone System work with Vonage?
• How to request support from 3CX
• How to convert a Cisco 7940 from SCCP to SIP
• What VOIP Providers have you tested 3CX Phone System with?
• Build History
• Does 3CX Phone System work with BroadVoice?
• Analyzing a SIP call