not sure, but if you've got a 3g phone, there are 2 different ways of connecting, via GPRS and via 3G dpending on your coverage. GPRS can go thrpugh normal mobile signal, 3G is faster but requires 3G coverage to work.
This might be the difference, but it might not.
just to clear up any confusion, WAP stands for Wireless Application Protocol and is nothing to do with access points. It generally refers to sites that render specifically for mobile devices.
forgot to add...
essentially, some wireless access calls are a set fee to browse and may cost a certain amount per session (the WAP on your bill), whereas some calls are charged on a 'information downloaded' basis (the INTERNET charges on your bill).