Kimi ni shika Kikoenai, Orange Recommendations
The 2007 version of the manga with the same name.
Both have similar themes and plots. In Kimi ni Shika Kikoenai, a girl, unable to get her own cellphone, imagines one in her mind. But suddenly, someone actually calls her--a woman; she also ends up talking with a boy whom she ends up having feelings for. Both manga have tragic elements and also have characters where the main character's future self contacts them.