There is an interesting article titled Will Amazon Be Your Phone Company? Many telcos are utilizing Amazon EC2 services. "Everyone from Aculab to Metaswitch are using Amazon's cloud. You can even get a hosted version of Microsoft Lync with voice support on Amazon."
"Aculab is sweetening the pot by offering services for just one penny per minute for both inbound and outbound calls." Interesting because their OPEX costs of being in the cloud are reduced.
Digium's Asterisk is in the cloud, not just at Asterisk, but in "containers" by Cbeyond.
Why do I bring it up? Two reasons. One is awareness. Know what is out there. Two is that YOU can reduce costs by going to IAAS and PAAS services like EC2. I know. I know. The control.