Just a quick headsup!
I'm not sure if this applies to other mobile providers or just for new Voda contracts in the last 3 months or so. I got this info from my cousin who works for voda, so it's genuine.
Basically, all calls are charged at a minimum of one minute now, so if you call someone and get through to the answerphone for 0.5 secs and put the phone down, that's classed as a one minute call, or you lose 1 minute talk time anyways. It's worse when you try to call the same person 5 times in a row and can't get through, that's 5 minutes of your talk time gone! We've all been there haven't we?