The Beijing Subway and bus passes are very conveniently obtained at almost every service counter in the subway stations. Whereas it doesn’t save you money taking the MTR (though a lot of time queueing up for a ticket), on many busses it will give you a more favorable fare swiping your card (e.g. RMB 0,40 instead of the standard fare of RMB 1).
Just go to the MTR service counter and ask them to issue the Beijing Transportation Card (yikatong 一卡通) . This card is sometimes also called „Traffic Card“ (jiaotongka 交通卡).
You can then charge your card either directly at the counter or at one of the machines in the station. Although many taxi companies claim to accept the yikatong, the fewest taxi drivers are happy or willing to accept it.