This prompt reminds me of the Lake House, a very stunning film about two people falling in love but living two years apart. If a service such as sending messages to someone in the future were possible, it would mean that sending a letter back would be possible, as well, for the usage of the same time-stream would fold back into either past or future; alternatively open at both ends. Since I do not know who I may befriend along the way, this service would have to provide a list of people I would come to know; if not, able to provide future addresses either of those I know or myself, for the future is subjective to what one decide, is it not? It can always change, based on one’s decision. The service has to keep track of that. So many things to think about, such as crucial information about the future for now to try and change whatever hammers. Terrorism would be mainstream. Unorthodox relationships such as depicted in the film, yet with a happy and relatively solvable ending. The same as the movie, Déjà vu, about people only seeing back in time to solve murders or crimes as it happened. Or I could be as simple as this lovely rainy day and just write a letter to myself, reminding the future me to put the milk back in the fridge after making a mug of coffee . . . would spare him the hassle of purchasing another bottle of fresh milk, so on and so on, continuum of history, so forth and so on! Interesting subject.
That is all . . .