This is a kind Telegraph using redstone clocks to record and store, (in a way) So let's get to it.
First you need to make a building, at smallest 16 blocks by 5 blocks, and make it look like a post office or something.
Next, make a long hole in a wall. It must be 12 blocks long for a building 16 by 5 (If you made a building bigger, leave four block on the wall or make space somewhere else). You MUST have space for four blocks.
Place repeaters along the hole on full delay.
Hook up to a redstone clock (the bigger the better). A good way to save space is to go up down up down in rows.
That will be the storer.
Next is the Sender, place a lever on one of the spaces. It's good to have a sign on top saying Sender.
After that, make a line of repeaters on full delay to the other telegraph office (A good way to do this is to go block repeater block so on) to make a turn place a block then, place a repeater facing the towards the place. Hook up to redstone the clock on the other one.
To use the Sender do it in Morse code, To make a Dot, turn on then off as fast you can, To make a Dash turn On count to three then off again.
Next is the Deleter, Place blocks in the clock with sticky pistons touching them when on so you can take them out of the clock stopping the pulse (Make it so it won't break things just take the block out)
Now the Canceller, Let's say you were sending a telegram and you made a mistake, Oh no how do I stop it, just make a deleter, good to make lots up the track, as with the Clock.
That's it all done
Can leave messages.
Easy to use.
Needs lots of repeaters.
Morse code Needed.
Lags a fair bit (Good way to stop this is to keep it well lit in the redstone clock.)
Needs a large Clock to do 7 letters word.
Good to have a Morse code up some where.
Write it out on paper.
Place signs on top of levers
Nice touch is to hook note blocks up to the line, not the clock.