On Phonebooth Free, All inbound calling whether forwarded or not count towards the minute cap. Most people think that it should be less cost, if the call is forwarded, but this is actually the opposite. When an inbound call comes into our system, we then make outbound calls based on your user's rules and then initiate a second call. Once the second call connects, we conference them together. So in essence we are supporting two calls for every forwarded call. We only treat this as one call and only track the single call minutes.
Once the minute cap is reached, calls will no longer forward.