AccuGlobe (http://www.accuglobe.com) offers a nice calling card product that I've used for a long time. There is a $1 monthly fee, but it's only charged in months you use the card. Six-second billing with a 30-second minimum makes it quite attractive. The rate for calling from Hong Kong to the US is 17.9 cents per minute. http://accuglobe.com/internationalorigination.html

The other calling card I like for international use is the Sam's Club AT&T prepaid card--it's great because it can be reached from anywhere you can get an AT&T operator.