Hi,
If Kamailio is the registrar, what role does it play in call routing?
For example, if a call hits FS and I instruct FS to bridge to a user,
how is that performed? Or does all call routing now need to be performed
on Kamailio, since it's the one that's aware of where users are (and
their associated presence)?
You can configure Kamailio and Freeswitch in anyway you need, Kamailio can be call router, freeswitch can be call router and both of them simultaneously can be call routers :)
Then users location DB will be in Kamilio and information regarding users will be stored in Kamailio, so Freeswitch will not know where user located and all calls between extensions will go through Freeswitch and then will be looped back to Kamailio and Kamailio will decide where to route call.
So in this case Kamailio is call router and it decides where to route calls, for example 44 prefix is routed to "vbox"(voicemail).
Nevertheless you can add some additional routing on Freeswitch too if necessary, for example if you need to send calls to PSTN and you need transcoding.
Nevertheless it is still possible to route PSTN calls directly from Kamailio too, without freeswitch.
With kind regards,