Since the combined speed of electormagnetic waves can be 'c' and that they travel in space at 'c' leaves no component for time, hence the time on a watch on a beam of electromagnetic wave does not change at all. With this understanding, assume two stationary mobile phone users U1 and U2. U1's mobile phone emits an electromagnetic wave at time T1 which according to U2's watch reaches him at T2. However, as per the wave, it is still time T1. Considering spacetime to be a book with events in a region of space R being arranged as pages of the book according to the time at which they occured (T1 and T2 are 2 different pages of the book), U1 and U2 have moved to the page corresponding to time T2 while the wave always remains in the page correspoding to time T1. Now how are the two users U1 and U2 ever able to communicate with each other? The wave and the recepient are never on the same page of the spacetime book.