Multiple url filter list in fortigate

What you can do is SSH to the Active unit, then run:

execute ha manage <x>

where x is the ID of the other unit.

Then run

config system interface
edit "port1"
set status down
next 
edit "port1"
set status up
end

You can then log on to the switch (assuming it is logging interface UP/DOWNS) and see which interface went down.

The Fortigate has the most advanced SIP protection of any firewall I have seen. It does remove the need for an SBC if your concerns are solely security.

What a Fortigate will not do, which an SBC does, is to transcode the voice codecs, but this is probably not needed in your environment.

There are two SIP ALGs in the FortiGate, one is a basic session helper and is on by default. This takes care of any NAT problems but does not address security. The second is to apply a VoiP profile to your SIP traffic. With this VoiP profile you have a huge amount of granularity on what you can do in the way of protection, but this granularity is only visible and settable via CLI.