Sentence:  If you want to keep the phone bill down you can set up your Newsreader to operate <WSD>offline</WSD>. This means that your Newsreader will fetch new message headers, collect messages you wish to read, and send any responses you may have set up all in one go. You can then read news <WSD>offline</WSD>, while you are not running up the phone bill[…]. 
Meaning of the word marked with <WSD> tags:  While offline; with an offline system.