Payment system in modern public transport

In addition to tradition payment system, that is through cash, there can be other systems of payment in public transport. This is to facilitate public, for that they should not have hastle of carrying cash. For example in Skane a county in south of Sweden. There are following payments at public disposal to choose from.
1. Payment through there mobile. That us instant purchase of tickets by sending an SMS through mobile.
2. Payment through any bank card.
3. Payment through transport company's own card( public can get 20% discount by using this form of payment)
4. Buying transport company's monthly card. This is most cheapest even if you have to use public transport even for one time.