What happens if nobody answers?

Unanswered calls are completely free.

Busy signals, ring-out with no pickup and failed connections never deduct credit. You are charged only for connected calls, with a 1-minute minimum — so a 5-second "hello, wrong number" rounds up to 60 seconds, but a phone that simply rang out costs nothing.

Note that if you get connected to voicemail, that counts as a connection and your credits will be deducted.