Hi James,
Cost is indeed a major component that set forward the economy of the operations,I would really like to put forward a suggestion to you ie You can consider Migrating to VoIP if the destination is US(If you are handling calls & making Calls to US) a VoiP back bone will be apt rather than IPLC. As you are aware VoIP is one of the most emerging & economical medium where in you can maintain the lowest of the cost and the Best of the Voice quality.
Thanks
Kris