hi,

> I suppose this is not yet supported by the iconv implementation, neither
> in NetBSD 3 nor NetBSD-current?

NetBSD 4 and -current already supports TIS620.
if you use NetBSD 3.1, use ISO8859-11 instead(ISO8859-11 == TIS620).
or rebuild encoding-alias database by following instruction:

$ su -
# cd /usr/share/i18n/esdb
# echo "tis620 ISO-8859-11" >>esdb.alias
# mkesdb -m -o esdb.alias.db esdb.alias

very truly yours.
-- 
Takehiko NOZAKI<tnozaki@NetBSD.org>