 If you liked
Hoshi no Koe
|
 ...then you might like
Natsu e no Tunnel, Sayonara no Deguchi
|
While Hoshi no Koe is just a short, and natsu e no tunnel is a movie, both have very similar themes.. Both contain:
-two friends trying to stay in touch via cell phone messages despite being separated by time differences
Hoshi no koe is a bit more sci-fi with the space aspect, while sayonara no deguchi has the vibe/setting of something like your name or any other recent makoto shinkai movie
If you liked one, you'll probably like the other!