Girls-High, which started in 2001, shows the trend of the era.
A city girl says "Anybody has a cellphone these days" while main girls from the countryside don't have ones.
In 2001, the situation was like, "most of highschoolers get cellphones when they enter highscools."
Cellphones' penetration rate in Japan:
Patlabor the Movie 2, 1993 : 3.2%
The End of Evangelion, 1997 : 46.0% ( PHS: 15.3%)
Love & Pop, 1998 : 57.7% ( PHS: 13.1%)
When the original novel of Love & Pop was written, I suppose most highschool girls didn't have cellphones.