since
it does not do media processing, but can be a sip signaling application
server and it is a lot you can do with signaling only (e.g., messaging,
presence, custom communications and notifications).
However if you mean a "IMS SIP
proxy/registrar" then OpenSer/Kamailio
could be valid (except for some custom requeriments of IMS). You can
take a look to OpenIMS which is OpenSer/Kamailio with some
"customization" or new modules designed for IMS.
This is indeed an app to look at, site is
http://www.openimscore.org.
AFAIK, they updated their code and practically they run same core and
common modules as kamailio/ser 3.0
To give the proper answer to the question, then the kind of application
wanted to be deployed must be described.
And kamailio is just the new name of openser, since there were some
trademark issues with openser word. The sourceforge devel project still
keeps openser name. Last version released under openser name was 1.3.x,
the first under kamailio name was the next one 1.4.0. Version 3.0.x is
the last stable one, with lot of enhancements since last version with
openser name was released, see here what are the major enhancements
coming with every release:
http://www.kamailio.org/dokuwiki/doku.php#features