Asterisk with analog pabx and four PSTN lines


On our company we are looking on installing a server with asterisk, but i have a few questions. Today we have four PSTN lines connected to a analog pabx system, and twelve ramals conected to the same pabx. What i want to do is setup a asterisk box and conect it to one ramal of the analog pabx, so if someone wants to make a voip call, it would dial the asterisk box ramal on the analog pabx (say 22) and then get a tone, to call using Broadvoice for example. On the other hand, i would like to call from a regular or cell phone to my company PSTN number and then someone would transfer the call to ramal 22 (asterisk) and then i would dial the same way that from inside the company.

It would also be good to be able to receive voip (FWD or Broadvoice) calls on the asterisk box, and asterisk transfers the call to a main ramal of my analog pabx.

So is it possible with asterisk?? What do i need to buy to make this kind of thing works? A FXO card or a FXS card??

I want to connect the analog pabx with asterisk this way so i will not need to buy expensives ipphones and stuff like that, i now we only need to make/receive one (or two) voip calls at a time.

Thanks a lot for any help.


With the money you save with Asterisk, go buy IP phones and
replace your whole PBX.

It’s not worth the effort to hack things together when you can get
good multiline SIP phones for $100 to $300 US. Then sell your old
system and phones on Ebay.

Lee Marzke