This proabably isn't major savings, but from what I noticed is that everyone is switching over to longer and longer call centers. However, there is a savior and it goes by the name of Skype. I recently got Skype to do English teaching and ALT job interviews, but I have to give the devil its credit when due: Skype will save you minutes off of call center hell.
Call center hell is when you are put through an automated system and you are forced to hear almost all the options of the billing information. (Whoever invented this is a bad bad man. =( ) I actually lost about 14 minutes (about $1.50 give or take some change) of my minutes and my life. While I can't be reimbursed or the latter, I can pass on who to use Skype which will save tons of money off of International calling and--you guessed it! Call centers. First sign up at http://www.skype.com/ and get a user name. To call all landlines, you can pay Skype roughly $30 for that as an annual service I believe. If you're on a pay-as-you-go minute plan like me, this would actually be worth checking into. There is also one more service called the Magic Jack, but I believe it is only useful in the United States. I would seriously get one if I was trying to leave for Japan.
For everytime you use a call center, a kitten dies... Please, think of the kittens.