They work mostly with modem surfers, by disconnecting them and connecting to a new line and billing significantly more per minute ( like phone sex ).
They are a good way to make money from surfers who don't have credit cards or their cards are not accepted.
More and more surfers are moving to broadbank nowadays, so dialers are getting less important for the adult biz.
But still some money can be made with them.
I recommend the
Money Tree Dialer 