Most advanced markets have the concept of flat fee conferencing, where in the subscriber just pays a fixed fee for the whole month or the whole year and enjoys unlimited conferencing capacity.
This helps in numerous ways, especially for the ones who are on conference calls day in and day out.
You don't have to worry about increasing your conferencing bills, by conferencing often. As you know in advance this is bill that will be due every month, yet doesn't limit from conferencing as and when you require to do so.
It saves you time , as you don't have to check your bills every month for any kind of discrepancies, as you know whether you use it a bit or a lot, it doesn't matter, you pay a nominal fees.
You don't have to worry about answering to your management about over usage of resources, all you need to do is worry about doing your work well.