Hello Si,
I can understand it's troubling having a seemingly short call being charged as a longer length of time. However, you should note the airtime charges (plus long distance, if applicable) apply to completed or answered calls from the moment you press SEND until you press END and includes the ring time (taken from Terms & Conditions; Section 3g). On the other hand, your phone likely starts its call counter once the recipient picks up. While people have argued that the time spent ringing isn't actual call time, it is considered airtime.
In addition to ring time, there are other sources of airtime which are not considered by a phone's call counter -- post-dialling delay, answer-signal delay and call-release delay (see here). Most, if not all, calls would be via voIP and the protocols required to establish calls take time to connect calls (see here). Furthermore, multiple switches and gateways involved in setting up an international call can also add additional post-dialling delay time.
You should also note that local and long distance airtime charges are rounded up to the next full minute (T & C; 3g). For example, a 61 second call would be rounded up to two minutes. If you take into consideration ring time, the various delays, and call time, it's very possible to exceed the minute cut-off and therefore the charges are rounded up.
Hope this helps 😀
Cheers
