#!/usr/bin/perl

use Encode;

# Perl char string (UTF-8) - i.e. your input
# (this is the Russian word - literal UTF-8 chars wouldn't be displayed
#  correctly in PerlMonks <code> blocks - thus here as \x{....} )
my $str = "\x{0442}\x{0435}\x{0441}\x{0442}";  

my $utf16 = encode("UTF-16be", $str);

my $sms = unpack "H*", $utf16;

print "$sms\n";   # "0442043504410442"