Electronic Voice Services is a different type of VoIP provider. While they do provide minutes and a softphone with their ZoomCalls VoIP service, Electronic Voice Systems offers a premium power dialing and call center service; the ZoomCalls service is intended to support use of the power dialing software.
Electronic Voice Service's bread-and-butter is their many-aliased power dialing/power seller software.
For instance, Electronic Voice Service's Power Dialer goes by different names based on the service type you use it with: with a landline or premise-based PBX, you'd use the Cheetah Power Seller; with VoIP in general, you'd use the Dolphin Power Seller; with Skype, you'd use the Green Mamba Power Seller. (Why it's not a black mamba, I do not know.)
For use with these and other of Electronic Voice Services's calling software (all with animal names), EVS provides ZoomCalls: a flat-rate softphone VoIP service where you pay for only the minutes you need and only the minutes you use. These minutes are allowed in addition to your current VoIP phone service (in case you have a fair use limit or have trouble integrating the Power Dialing service with your VoIP service). Electronic Voice Services doesn't offer any bells and whistles with these minutes, just the ability to call - oh, and to use their powerful selling software (which is pretty impressive stuff).