How did the telephone advanced?

Since it's invention many improvements have been made as technology has progressed.

The sound quality was improved by using better designs of microphone and receiver.

The automatic telephone exchange was invented, to allow people to dial anywhere on their own without human intervention.

The LD (Loop Disconnect) system of pulse dialing was replaced by the DTMF (Dual Tone Multi Frequency) tone dialling, to allow more automated and faster connections.

Now radio is used to allow phones to be truly portable.

The use of computers in phones have allowed more features to be incorporated at modest price. Like cameras, internet, planners, bluetooth, etc.