ダイアの約束～逢いたくて～

Main character is busy working at a famous toy making company. One night he receives a letter from home together with his favorite phone toy from the childhood. Suddenly toy phone starts to ring even though it has no batteries. Girl voice from the other reality says that promise must be kept and that she's going to be protagonist's wife. The next day his childhood friend visits his room, but the hidden reason for this visit becomes clear much later...

[From vndbreview]