I am interested in using the Open Source Asterisk PBX VOIP Software as a replacement for an older POTS/PSTN system. My goal is to reduce their overall cost of ownership. I am trying to get a better understanding of this software. How is this physically done. My understanding is a such:

First scenario: Asterisk VOIP/PBX connecting to an older digital/analog PBX system:

10 VOIP phones - to replace older digital or analog phones!
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(System that connects to older analog/digital PBX system essentially as analog telephone adapter(ATA) for analog phones)
PC/Server/5 Digium cards - Converts older analog/digital voice data to proper format for VOIP (Exchange)company. The Digium cards are responsible for conversion from and to (FXS & FXO) Foreign Xchange Station and Office (Call & Receive) through older PBX Hardware.
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Internet to VOIP Company
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Receiving companies older POTS/PSTN PBX or VOIP system.

Scenario 2:

10 VOIP phones
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24 port Asterisk VOIP SERVER that connects to T1,ISDN,DSL and etc..)
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Internet to VOIP Company
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Receiving companies older POTS/PSTN PBX or VOIP system.

Am I correct.

Hi metallica,


Thanks for your post.

I also need some understanding about physical settings needed on the asterisk machine and VOIP server