I want to known about the transmission of electromagnetic waves in cell phones is digital or analog signal ? Explain me about the transmission line ?

You mean the radiation used to communicate between a phone and the mast?

Cell phones have used both digital and analog technology over the years; these days it is much more likely that you will be communicating over a digital transmission than an analog one. There are several different multiplexing algorithms used in digital transmission and this depends on what format your carrier supports, one example is CDMA (Code Division Multiple Access). I suggest you do some reading on wikipedia regarding this because simply asking for an explanation isn't exactly an easy thing to give a reply to. There are high level university communications and electrical engineering courses that cover topics like wireless transmission.