There is this yaoi I read once and it was a part when both of them in rush hour train, and suddenly the cell phone vibrate and stir his desire.

If im not wrongly remember, the one who call them is the school principal.

If I'm not mistaken the manga you are looking for is Shinyuu Henjou!
The scene you are looking for happens in chapter three on page 26 to 28.

Remembrance, a forsaken thing that revokes ignorance and leaves people in doubt, is my only redemption and solace deep within the cascade of white.

The evergreen trees speak of days long past when music mingled with the wind and sweet murmurs brushed our cheeks.