In order to survive financially Bell had to work on the musical telegraph, but he also continued working on his mechanical voice transmitter. On that summer afternoon in 1875, when Alexander heard the first sound transmitted over his machine, he realised that he had finally achieved his goal. Almost a year later, in March 1876, the first words were heard coming through the phone.
On his 29th birthday Alexander Graham Bell registered his invention with the patent office and, because they had never seen anything like it before, they registered his invention as 'an improvement in telegraphy'. The name 'telephone' came later.