OpenSRF was developed using jabberd-2.0s4. There are two patches that we applied to this source. The first patch allows a config setting which disables offline storage of messages (see http://www.marquard.net/jabber/). This patch is required for OpenSRF to function. The other patch fixes a segfault in some xml entity escape code.
See http://open-ils.org/cgi-bin/viewcvs.cgi/ILS/OpenSRF/src/patch/README?rev=220.127.116.11&view=auto for more info on the replacement files.
Note that future versions of jabberd2 have likely fixed the segfault issue, however the offline patch will not compile in the newer jabberd2 versions we've tried :).
Long story short, any modern version of jabberd2 should work fine so long as offline storage can be disabled somehow.