Two small communities are separated by a distance of three miles. In the absence of a modern telecommunications infrastructure, think of five ways for inhabitants to efficiently exchange messages.
The first method that comes to mind involves physically carrying messages on foot or in a vehicle of some sort, and relaying them verbally or in written form. 

An alternative approach still involving physical delivery of the message could be to employ some physical system to convey the messages for you. Examples of this principle include zip lines or pneumatic tubes.

A different approach could be to transmit the message acoustically, which at this distance would require a very loud signalling device, the assistance of a transmission medium of some sort, or repeaters along the way.

Encoding the information of the message and transmitting it visually provides yet a different approach. This could be in the form of light flashing or smoke signals for example. 

Finally, employing some rudimentary physical system to transmit encoded information could be used. For example, a taut cable or hydraulic system whose changes or movements could be translated into information.