Your calls per second (CPS) allowance defines the number of outbound calls you can initiate every second. By default, each account can initiate one call per second. Contact the Plivo sales team if you need a higher CPS limit for your account.
There are no limitations to the number of concurrent calls you can make using Zentrunk. Zentrunk servers are elastic in nature — they can scale up or down depending on call traffic. No additional configurations are required to add more capacity.
Zentrunk SIP trunks are charged on a pay-as-you-go basis; you're charged only for the minutes you use.