The Billing mechanism employed depends on the country of the client, typically using PSMS (Premium SMS) as a billing mechanism.
It is expensive (ie the cellcos keep a big chuck) but, hell, money is money
You should consider sending such traffic to a cell phone friendly affiliate proggie like
www.sex-goes-mobile.com
If you would like to create your own wapsites, check out
www.wapple.net, for billing
www.bango.net
Yes, the iPhone has rendered Wapsites obsolete, but there are still plenty of people out there that do not have one.
Hope this helps.