If you have two phone lines (dial tone from a phone company) and whant to extend those dial tones over the internet you need:
1 FXO device with two ports. This device will go into the site where you have the two phone lines coming from the phone company.
1 FXS device, two ports. This is the device that will attach to the phones and to the internet on the remote end. The device provides power to the analog phone sets, as well as ringing voltage.
One good device to get this doen is the Quintum A200. It does have two FXO ‘s and two FXS per unit. You could use them “point to point ” over the internet without a gatekeeper.
You will be looking around $1000.00 american dollars on equipment cost.
There are cheaper solutions out there. Look for FXO and FXS gateways.