As I already complained, spammers seem to like my phone database. It has not been a major problem so far, but I started to get about ten invalid records per day.
This forced be to find automatic solution to get rid of this. Inspired by recent article on root.cz, I wrote simmilar solution as is used on php.vrana.cz. It should not harm regullar users who have javascript enabled, others will have to fill in one extra field.