Move-Add-Change services are in place to make sure that organizations can both manage and control the merging of people and their assetts, especially allowing for proactive planning when times of corporate change might precipitate. Move-Add-Change needs may vary, whether they involve a person or a piece of hardware. For instance, MAC might be of importance when a company is looking to “move” a desktop phone to another location, “add” a new piece of hardware to that existing system, or even “change” the employee's name assigned to that particular phone. In this case, the three actions are related and not mutually exclusively, collectively making sure that the system 'works'.

These are primary needs in any IT (i.e. VoIP) service sector, where moves, additions, and changes are monumental components to creating a sturdy and efficient IT infrastructure.  Most desired are simple software changes, however, this is not always the case. Theoreticals where more attention might be needed are, if an individual relocates to a building without VoIP service or even moves to a non-VoIP desk location. Relevant charges apply, and seldom will a company's internal team take care of MAC unless it is simple and not time consuming. These three elements are instrumental for any business to keep up in a dynamic business world:

Move: Will most typically entail the physical relocation of hardware, equipment, and devices. It is not as easy as it seems, and often involves many more complexities than merely picking something up and putting it down elsewhere. Connections must be removed carefully, devices must be uninstalled, and they must be packaged properly before being shipped to a new facility or location. Failure to adhere to this step could result in damage to expensive and essential equipment, setting companies back financially and chronologically. 

​Add: The business world is ever changing, and to keep pace, tools within a business must also follow suit. As such, infrastructure must constantly be upgraded, which might include the upgrading and enhancement of new hardware or software platforms. This might also be the introduction of new hardware, and additions are mostly in an effort to maximize the output of your business. The end goal is usually to find the most cost-effective and operationally efficient solution, while software upgrades take the brunt of the installation, training, and appropriate documentation.

Change: Change services would particularly involve hardware or software mods, along with replacement. When a device becomes worn out or is “on the fritz”, it's clearly time to institute change. Businesses might apply a single piece of hardware, or even revamp a whole system. Change is more concerned with building on existing systems, setting new configurations, backing up data, and setting recovery. This method is preventative and also after the fact, fixing a system so that i may endure without physically removing it.

MAC services usually involve agencies which specialize in the above three, where a company might contract them to come in and apply one or even all of them. The process is usually not instant, as approval for any of these elements might be required before a company goes forth and has them executed. MAC services are like IT movers, making sure everything is in place and functional, taking the strain off a business and ensuring they may move forward as they did before. 

Related:
What is Geolocation?
What is Colocation?
Network Address Translation
What is Fault-tolerant design