There are loads of threads here dating years back about BB members' experiences with HypnoBirthing Just do a search and they'll all come up!
Calmbirthing is one up on HB because of it's physiological emphasis. The difference (apart from language used - one's for US audiences and the other for Oz) is that CB is from a midwifery perspective, with the visualisations etc and HB is writte by a hypnotherapist, not a birth/pregnancy caregiver. I loved my HB course, and the advantage was that the practitioner is also a doula (so has that physiological experience and education), as well as a counsellor with HB and Emotional Freedom Technique under her belt