Todd, the ATA 186 is a FXS type of device.That means that internally it SUPLIES dc voltage to the interface,like to feed a phone type of instrument or device.If you connect a ATA 186 to the phone line coming from a PBX or a Central Office ,most likely the ringing voltage from the C.O. will fry it.
In principle you will need a FXO type of device to connect to you phone like. Something like a one or two port gateway with FXO interface. That will do the conversion from normal phone line to I.P. or internet on the other side of the box.
At the other location you will need a I.P. phone or a FXS gateway that reverses the process.
Look for a one or two port gateway that will do “peer to peer”.That means that it will not requiere a third element call the call manager or the gatekkeper to stablish the call betwen the two boxes.
That is if both places have static I.P. addreses. If you could only get dinamic or PPOE addresses, you will need the third element or gatekkeper to kkep track of the changing I.P. addressses of your terminals.
Good luck to you.!!!!!!