Indeed, utf is the way to go as soon as you use non-english text, if you required portability. Don't forget to utf5_encode either.
The t61_8859 functions seem to be deprecated.
(PHP 4 >= 4.0.2, PHP 5)
ldap_t61_to_8859 — ترجمه کاراکترهای t61 به کاراکترهای 8859
This function is currently not documented; only its argument list is available.