Presence allows one UA to "watch" others by subscribing to related event packages.
FreeSWITCH supports presence out of the box.
On the client side, if you use xlite/eyebeam, create a new contact and check "show this contact's availability". It should then SUBSCRIBE to that contact and start getting NOTIFY messages like this:
Use FreeSWITCH as a client
FreeSWITCH can work as a client to SUBSCRIBE to a server (another FreeSWITCH), to enable this, add a subscriptions section to your gateway config, e.g.
Note, FreeSWITCH(server) also supports *dialog* events beside presence. eventlist is not supported (on server side) at this time.
On getting NOTIFY, a NOTIFY_IN event will be fired.