"Analog - The most basic type where voice is simply transmitted to another receiver with no conversion. Analog is to record players as digital is to CDs. Analog phones may have low sound quality and be more vulnerable to interference and eavesdropping.
Digital ? Voice is converted to a digital format before transmission. Because it is digital, certain unwanted noise can be filtered out to reduce inference and unwanted background noise. Digital phones are more secure and less prone to interference because they use codes that help prevent other devices from capturing the signal. " <--- copied from the web
A digital phone uses a digital signal from the phone to the handset, longer range and less chance of being listened to. Digital is better
This has nothing to do with a digital or analog phone line.