If the communication is sensitive or time-critical - or you're sending a "wave" (see below) - then the above broadcast methods are used. But most other long-distance (e.g. interstellar) communication usually involves some type of physical storage medium accompanied by a physical cover letter. When it's going to take a minimum of 168 hours to get there anyway, why not send something you actually touched to the recipient?

Wave: Also known as a "ripple," this is an attempt to contact a jump-mobile recipient. It's sent in several directions at once, based on the sender's best guess as to where the recipient *might* be, over the course of a range of future dates. Each possible destination (usually a starport) holds a time-stamped copy of the wave until the intended recipient calls for it or a designated purge point is reached. [And yes, I stole this from Firefly].