I mentioned about Finger Five, that kiddie singing group, when I wrote about "Gakuen Tengoku" （学園天国）all those months ago. And I only found out a few minutes ago, but I didn't even give them their own label on the side there, although they were the original singers of the song with Kyoko Koizumi（小泉今日子） covering it years later.
To rectify that oversight and to give them a bit more of their due than I did for "Gakuen Tengoku", allow me a little background on them. The Tamamoto Brothers（玉元） from Okinawa started their singing lives as All Brothers in 1967; at that time, it was just the three siblings of Kazuo（一夫）, Mitsuo（光男） and Masao（正男）. I mentioned in the other article that they reminded me a bit of The Osmond Brothers from the United States whose littlest brother Jimmy had his own brief success in Japan as well. Well, according to the Wikipedia article, they would do covers of The Jackson 5 and also had some inspiration from The Partridge Family, although that was a TV-invented group. The three brothers decided to strike it big in Tokyo and signed up with King Records in 1970; they would change their name to The Baby Brothers. However, their three singles with King didn't sell well, so they did a bit of a reboot by recruiting their brother, Akira（晃）, and little sister, Taeko（妙子）, and then switching over to Philips in 1972. Of course, there was that final name change to Finger Five.
The reboot worked and the records started selling like hotcakes. Their 2nd single with the new label proved to be their first big hit, "Kojin Jugyo"（個人授業...Private Lessons）which sold over 1.4 million records when it was released in August 1973. But their biggest success came later in December of that year with "Koi no Dial 6700" (Love Call 6700) with that old-style phone, Taeko giving the cute response of "Hello, darling" and the boys launching their "Ring, ring, ring..." becoming one of the more recognizable intros of a kayo kyoku.
From that video above, Finger Five seemed to not only emulate those above-mentioned American groups in song but also in fashion. I vaguely remember seeing them on TV as a very young kid myself but my first sight of them was actually through the pages of one of those thick pulp manga . The group had become so popular that they were getting depicted in that medium as well.
In any case, "Koi no Dial 6700" became a monster hit with it hitting No. 1 right on New Year's Eve 1973 and staying there for another 3 weeks. It sold 1.6 million records and was also another hit for lyricist Yu Aku（阿久悠） and composer Tadao Inoue（井上忠夫）. It eventually became the 4th-ranked single for 1974.
As for what happened to Finger Five, they would release a total of 22 singles and 7 albums with the final single coming out in June 1978. Since then, the group has popped up a number of times under various names to get another shot at glory only to get more curiosity than adulation. But in 2003, they got together for a 30th anniversary concert which brought in their fans from all over the country.
A number of cover versions of "Koi no Dial 6700" have been performed, including one by the group Dream5 which released their version in January 2011. It peaked at No. 20 on Oricon.