Hi Fabio,
For what i read now Osmocom have 2 software BTS
(Osmo-BTS and Soft-BTS),
communicating with the A-BIS over IP interface to OpenBSC:
http://lists.gnumonks.org/pipermail/openbsc/2011-March/002529.html
http://lists.gnumonks.org/pipermail/openbsc/2010-April/001508.html
Now we have two software BTS in developing phase, softBTS and
osmoBTS, In A-bis side, both communicating with OpenBSC using
ipaccess style A-bis over IP protocol. Probably difference would be in
Um side. I am not considering Universal Software Radio Peripheral as
hardware for softBTS, that mean no plans to use openBTS as bridge to
USRP.
fadil