Looks like the Solaris versions prior to the version 2.6 (SunOS 5.6) have a problem of year 2010.
Surprise, surprise! If the current date is specified, they just don't boot in a single user mode, hanging after detection of serial ports (zs1 is /obio/zs@0,0), when /devices directory should be configured.
At least the version 2.5.1 hangs when the system date is > 2009.12.20.
Going to update the howto....