Sipura Spa2000

That will be very easy with H323 gateways. I do not know about the Sipura, if they do H323 at all or not.

Do you need to connect phone to phone, or phone to PBX???

For “phone to phone” there are many small, cheap devices, like the Ericsson Web Switch 100 that will do the work for under $250 on both ends.

CO ports are what you would plug an FXS channel into ( think of an fxs port to be a phone line you would get from the telco ) and to attach to your extension ports you need FXO ports. 2 Sipura SPA-2000’s will not achieve the application that you are trying to create here. The sipura SPA-3000 has 1 FXS port and 1 FXO port integrated into the same unit. Here is a good explanation of the hardware you need:

Site A:

only extension ports are available for interfacing to the PBX. At this site you need to have an FXO device ( one or more ports ) that you can tie into the PBX as if it were another extension. You MUST be sure that the extension you are trying to interface to is not a digital system ( i.e. Nortel or panasonic or any larger systems ) unless you use an ATA to convert the digital port into an analog port.

Site B

You can choose whatever hardware you have availiable ( your SPA-2000’s are a nice choice here ) the SPA-2000’s must be tied into the PBX as if you bought more lines from the telco ( CO lines ). When your “remote users” dial these FXS lines, the associated CO trunk line will ring into the PBX.

Extra stuff needed?? yes.
you need a SIP proxy to manage the registration of the sip devices. I personally have had good experience with interactive Intelligence’s interaction sip proxy ( it’s 200 bucks ). There are other products out there that I know are free but a quick solution with a 5 minute install is worth it for me.

Any questions?

In my situation, my SIP Server connects to Azacall200 (Azatel’s SIP telephony adapter like a SPA2000).
so I can make a call from an analog phone to another SIP Client via ATA and Brekek OnDO SIP Server.