Series: Suzumiya Haruhi no Yuuutsu - Itsuki-kun's Cellphone. (Tokiomi Tsubasa)

Original title: 一樹くんの携帯。
Artist: Tokiomi Tsubasa
Source: Pixiv search

Mikuru is a tiny cellphone-girl owned by Koizumi. Expect lots of KoixMiku moe.