Just fine, I run Primus voip through mine and have various customers running sip, voip, h323, etc.. I generally set them up with guaranteed bandwidth for the voip traffic, or, I use prioritization to put all such traffic on high and the rest on medium priority.
I ended up looking on the Fortinet Knowledge center, and I found a post that said the following:
======================================= FortiGate Support for the SIP protocol
Support for Session Initiation Protocol (SIP) was added in FortiOS version 2.8 MR10 (build 465). Note that VIPs are not supported in MR10.
The attached technical note discusses FortiGate support for the SIP protocol and provides some sample scenarios and configuration examples.
If you are having difficulites with the connections, you may need to remove the session helper in MR10 to enable an SIP phone to work. ========================================
It looks like SIP support wasn't added until after 2.80, build393. Since I'm purchasing a previously owned unit, my guess is I'd have to sign up for a costly support contract to get VOIP/SIP to work. However, it appears even if I were to update, the update does not support VIP's which I use since I have only a single IP.
No VIP's in build 393?! I find that hard to believe, I'm sure I've got clients running them on MR10. Could they just mean no VIP is support for SIP? Anyway MR11 is current so you should use that. Man that's wacky enough I might just blow in MR10 on my FG60 and test it out myself, I flat don't believe that there is no VIP in MR10. I have access to a SIP gateway I can use (with some effort). Not sure I actually have *time* this week to do that, but if I do I'll let you know what I find out.
Anyway, I think firmware only contracts are cheap, as is 8x5 email support. It's AV, IPS, and Fortiguard subscriptions that cost the most. Talk to your nearest freindly reseller about your options.