Mou Hitotsu no Mirai wo.

Future gadgets lab - check Time Travel Cellphones - check Unintended Consequences - check The main difference is that one has cellphones that email to the past and the other has cellphones that call to the future. 

"World's End" / "Arata naru Sekai: Mirai-hen" and "Mou Hitotsu no Mirai wo." are two short anime that each focus on a form of time travel via pseudo-science. Though the tone and atmosphere are very different, the protagonists of both respective works are groups of good friends who do not seek out to do harm. 

"Arve Rezzle: Mechanized Fairies" / "Arve Rezzle: Kikaijikake no Yousei-tachi" and "Mou Hitotsu no Mirai wo." are short standalone science fiction works that involve an experiment or procedure having unintended consequences and thus resulting in an unfavourable outcome for the protagonists. These two anime both happen to feature a machine with a tank that the body rests in during its usage as well as a twist that leads up to a cliff-hanger ending. 

The character design feels similar! And the noise those phones make... Lol that aside, I can just offer my vague evaluation of how similar they feel..