How much does it cost to call one of those numbers from a BT phone?

What about other numbers beginning 08 or 09?
How much do those "unlimited weekend" tarriffs cost on a weekday?

BT ‘Unlimited Weekend’ package means 0870 and 0845 free, other packages you may pay for these call at certain times
09 are premium rate numbers and providers can charge whatever they want

Go to BT.com for info