If you'll rely heavily on conferencing services, you may be entitled to volume discounts. These discounts require you to commit to monthly minimums and you may be assessed penalties if you break the contract.
When you want to get multiple people from far off locations together for a meeting, a phone conference service can arrange a real-time meeting without travel hassles and expenses.
It eliminates the "he said, she said" finger pointing. It can also be a great way to train salespeople as conversations can be recorded for later analysis.