Time for the Stars by Robert A. Heinlein

 

Pairs of twins on earth are trained as telepathic modes of communication: one will embark on space travel and the other will stay earthside, and together they will transmit news and updates instantaneously across a trillion miles. Time, however, will pass more slowly for the twin travelling through space at a speed just below the speed of light, making for uneasy relationships between twins who started out the same age but end up vastly separated by time AND space. Interesting although not much happens.