Hi, I called Hipness the other day, and the phone number was working fine. I am not sure what went wrong for you, but it sucked.
Anyway, I would highly recommend you to call a bit before next time. In general cases, not all the girls are available when you call. As far as I understood their strategy, escort are generally working less than what is mentioned on their website. Sometimes I call and only one or two escorts are available...
I normally call 30 min before, and call again when I am in the love hotel.
Another thing I would advice is to book 80 min if you have time. 40 min is terribly short considering the time for shower, preliminaries and everything. Of course, it may vary according to people, but it is a pity not to really enjoy one hot girl just because the time is tickling. One of my best time with a thai escort was a 30 min hot massage.
Anyway, if you really want to stop using hipness, there is another thai girls escort website (thaigirl.jp). I haven't tried it yet because I really like hipness.
Hope you will have better luck next time!