Secure apt feature has been added to 0.5 and experimental repositories.  
Although apt-get complains about the key is missing, you could still be able to 
add the packages from voyage apt repository with the key.

To add the public key to apt key rings and get rid of the error messages:

# wget http://www.voyage.hk/dists/experimental/archive.key -O - | apt-key add -

 Name                    Last modified      Size  Description
 Parent Directory                             -   
 Packages                2010-02-22 12:13   64K  
 Packages.gz             2010-02-22 12:13   16K  
 Readme.txt              2008-06-03 09:27  370   
 Release                 2010-02-22 12:13  1.1K  
 Release.gpg             2010-02-22 12:13  197   
 Sources                 2010-02-22 12:13   12K  
 Sources.gz              2010-02-22 12:13  3.8K  
 aircrack-ng/            2007-03-20 00:48    -   
 alsa/                   2009-01-08 13:00    -   
 archive.key             2010-02-22 12:13  1.7K  
 atl1e/                  2009-01-08 13:00    -   
 atl2/                   2009-01-08 13:00    -   
 aufs/                   2009-01-08 12:59    -   
 awds/                   2008-06-26 00:40    -   
 batmand/                2008-02-29 00:58    -   
 bcm43xx-fwcutter/       2008-02-29 00:49    -   
 build.sh                2008-05-31 12:06  576   
 busybox/                2006-11-15 23:07    -   
 et131x/                 2009-01-08 13:00    -   
 frottle/                2006-01-05 00:14    -   
 haserl/                 2006-11-15 23:07    -   
 hostapd/                2006-07-16 00:29    -   
 ieee80211/              2007-03-20 00:49    -   
 ieee80211softmac/       2007-03-20 00:49    -   
 ipw2100/                2007-03-20 00:49    -   
 ipw2200/                2007-03-20 00:49    -   
 kernel/                 2007-03-21 00:28    -   
 libgea2/                2008-06-26 00:40    -   
 linux/                  2009-01-08 12:59    -   
 lzma/                   2009-01-08 13:00    -   
 madwifi-ifupdown/       2007-01-28 23:43    -   
 madwifi-ng/             2007-03-20 00:51    -   
 madwifi-tools/          2009-01-08 13:03    -   
 madwifi/                2009-01-08 12:58    -   
 maintainers.sh          2005-03-17 10:23  108   
 misdn/                  2010-02-22 12:13    -   
 ndiswrapper/            2009-01-08 12:58    -   
 nocatauth/              2005-07-15 23:14    -   
 nocatsplash/            2009-01-08 13:02    -   
 olsrd/                  2008-08-19 09:52    -   
 openssl/                2009-01-08 13:03    -   
 openswan/               2008-07-13 12:11    -   
 p910nd/                 2007-07-23 14:23    -   
 parprouted/             2006-07-16 00:29    -   
 rt2400/                 2007-03-20 00:54    -   
 rt2500/                 2007-03-20 00:54    -   
 rt2860/                 2009-01-08 12:56    -   
 squashfs/               2009-01-08 13:00    -   
 voyage-util/            2009-01-08 13:02    -   
 wavemon/                2007-03-20 00:54    -   
 wifidog/                2006-04-20 10:09    -   
 wireless-tools/         2008-07-13 12:12    -   
 wpasupplicant/          2006-07-16 00:29    -   
 zaptel/                 2009-01-08 12:59    -