Why can't the AT&T/Cingular,Verizon,Virgin mobile,Amp mobile,Boost mobile,T-mobile,Cricket phones and others charge customers with per second billing?

Why don't they charge people for the seconds they use,but instead,they convert seconds to minutes?
Why do we all have to pay for a minute when we actually make a thirty seconds call?
Y'all see what i'm driving at? Why should the conversion be rounded up instead of rounded down?

In most African countries,customers pay per second.Plz don't tell me that cellphone companies in Africa are helping out the poverty situation because we all know that cellphone companies are the last to help out.
And i know every cellphone user will be happy with PER SECOND BILLING.

I have Cingular with Rollover. I never run out of minutes, so it doesn't bother me.

I'd be paying the same amount anyway.