Must use software display to see the lights that show what the modem is doing. Connection much more prone to static and interference. Only a standard handset will fit. A digital modem does not have to convert between analog and digital signals. A digital modem is faster than an analog modem.
Digital modems are more expensive and so are digital data lines from the phone company.
The phone company has to install additional equipment for some kinds of digital modems. Normally a digital modem can receive data at a much higher rate than it can send it out. That works out fine for most people because they are only sending out a few responses instead of whole web pages or data files. It actually should be called a terminal adapter , but the name modem has stuck. 64 Kbps for a single line and 128 Kbps for a bonded dual line.