Internet access in Bejing

I assume that you ask for the internet access for your phone, right? If so, you need to choose a telecom operator according to your phone configuration. If it supports WCDMA, then you should buy a sim card from China Unicom. According to what I know, they provide different packages to foreigners and Chinese people. So you have to consult with the Unicom branches and choose a package according to your needs.