They both use the same means of transporting data.
Telegraph is merely dots and dashes (Morse code), or binary on off.
The difference is Bell worked out how to transmit oral (by mouth) sound, and for it to be received and converted into Aural (by ear) sound we hear.
Hence the microphone and head piece (speakers) on a head set for skype.
So the advance was being able to speak over the phone not listen to or interpret a load of dots and dashes.