I saw that there was an automatic reconnection mechanism implemented in Sip Communicator.
First of all, is it active in the Linux builds?
I tried the 2646 build on Debian Squeeze - i disconnected the VPN i use from home for my SIP and Jabber accounts on servers out internal network (there are no means to connect from outside to these accounts).
The Sip contacts dissapeared but the SIP and the Jabber accounts were "on".
The Jabber contacts stayed visible (and some online) as if i were connected still - the account and contacts finally got offline after a few minutes. But the last online contacts still remained on the list in offline state regardless that i set "hide offline contacts" (after toggling hide/unhide these contacts dissapeared).
After that a popup window said that "The Jabber server requested your authentication" asking for the Jabber password - It is not possible since the VPN is down and the server is not reachable from outside.
The SIP account stayed "on" - maybe waits for the 3600 s timeout or something? In older builds it got offline pretty quick after connection loss.
I tried to call a number via SIP and the call window just hang there at "connecting". It did not "fail" as it should have.
I reconnected the VPN and nothing happened. No accounts reconnected automatically. I reconnected manually the Jabber account - the contacts appeared, it was ok.
But the SIP contacts dissapeared from the list altogether - they were not even in the offline list - i disconnected and reconnected manually the SIP account but the contacts never came back, only after i restarted Sip Communicator.
The only real change i saw is that the annoying focus-grabbing notifications are gone - although some notifications should tell the user that a certain account is disconnected - maybe a systray popup or a toaster (the bottom right one) popup?