Good question...
here's the plan (such as it is)
sail-2.2.1-759 is/was the last of the 2.2.1 releases. If you wish to stay with Zaptel and Asterisk pre 1.4.23 then you can install the 2.2.3 release series (available shortly); this is essentially a "backport and patch" continuation of the 2.2.1-xxx line. At the moment, we backport most new features into 2.2.x but the plan is to gradually stabilize this release as DAHDI comes on stream in the 1.4.23 and higher asterisk releases.
For both zaptel and DAHDI releases, we've abandoned the old svn revision numbering in favour of a more formal release number. Hence release 2.2.3 began life as 2.2.3.1. Internally, we are up to 2.2.3.7 so there will have been at least 7 internal releases by the time we load it up to the webserver (there will still be bugs, there always are). For debugging and reporting purposes, the svn revision numbers are still documented in the rpm changelogs (I think we are up to around -800 now).
We will continue to support Zaptel Asterisk for the forseeable future because most of our customers are on Asterisk 1.4.21, which is the release on the SARK/SME 7.4 Distro. We don't tend to yum update live PBX servers "just because we can", the risks outweigh the rewards for a single application server. If they aren't broken, we don't fix them, which means that SAIL Zaptel/Asterisk will be around for quite a while yet.
Hope this helps
S