We want our clients to know what a broadcast is going to cost before it goes out, not after. We feel this keeps it simple. With credits, you have a simple cost per call. With per minute charges, some voicemail systems take 45 seconds before you can even hear the beep to leave a message. Additionally, per-minute charges open the door for all kinds of shady tricks - like rounding up call lengths in 30 or 60 second increments (instead of the industry-standard 6 seconds) or counting ring-time as part of the call length (carriers don’t charge for ring-time). We prefer to avoid tricks and gimmicks.