I'm just reading about the PBX and it's not clear how you handle multiple PSTN gateways for outbound calls. Could someone please explain to me how this works with 3CX? Image that you have 4 SPA-3000 ATAs providing outbound access on 4 PSTN lines? How do you tell the software to use whichever of the outbound lines is currently available? I see where you'd register the 4 gateways and I see where you'd create the outbound rule and assign it to a gateway, but how do you select a group of gateways? Do you have any control over the order in which the gateways are used? Thanks!