I just read
Kimi ni shika kikoenai (Only you can hear me)--or well, what's up of it--and it's really good. There's at least one more chapter, but I think the story ended with this one. I rather enjoyed it.
Short summary: A girl who has trouble speaking with others invents an imaginary cell-phone...and gets a call on it one day.
If you've got an hour or so, I'd say give it a try.