If only US perveyors of long distance and cell phones even had 30 second billing in the US! Pretty much all cell phone carriers charge in full minute increments and also charge as "send to end" meaning they bill for calls even the connection and ringing time before the end party answers. Carriers have the ability to charge as accurately as they choose to, but do not choose to do so since it uses lots more minutes with the combination of full minute increment billing combined with send-to-end billing will assure the most possible revenue for all calls. I dare say that if people were charged the actual usage in minutes many people could conceivably sign up for plans with less minutes allowed per month at a lower rate.
14 years ago