Scrying

Though once used more generally, in modern times scrying refers to a form of magical communication. Via specific spellwork and enchantment, some objects may be turned into scrying objects. The most common form of this is the scrying stone, which most magic-users and many other magical people possess. Though scrying is more commonly used to speak with someone far away, scrying stones can often send and receive messages as well.

Utility

Scrying is used for communication, especially across longer distances. In all forms scrying lets two people call each other, sending their spoken word to one another, and most scrying methods also communicate images, either as a flat image on a mirror or as a projected 3D image from an orb (like a scrying stone). Newer scrying stones, especially fancier models, can also send and receive messages by letting the user capture an image (or a short recording) and sending that even when the other user isn't active.
Naturally, as with most communication methods, misuse exists. People may use it to harass others, or sent unwanted or even graphic images. Some have even tried hijacking the network of scrying stones to send a call or message to all stones within a certain distance.

Manufacturing

Scrying requires, first and foremost, a specific and complex set of spellwork and enchantments. How and what is done, exactly, will depend on the item. A set of matched scrying objects is different from a scrying stone, after all, which connects to a larger network. And not all scrying stones are made equal, either, with a certain degree in variation, creating cheaper plainer models and fancier more complex models.

Social Impact

The wide-spread availability of scrying objects, and especially scrying stones, had huge impact on magical community. Suddenly communication was no longer dependent on having to meet someone face-to-face, or delivering mail to them. Scrying stone communication was not only private, but secretive, making it much easier to stay in touch with others without the risk of Mundane overseeing.
Those faraway, those unable to travel, those who were talking to others without their parents' permissions... Yes, the introduction of scrying stones truly revolutionized communication in the magical community.

Access & Availability

Though it is difficult to make a scrying object, never mind to connect it with others, they are widely available as pre-made items.

Complexity

Simple components, very complex spellwork.