Area code 364 was introduced in 2014 to much fanfare.
Officials with the Kentucky Public Service Commission had been working on a new area code for western Kentucky since 2006, when they announced [PDF] that a split of 270 would be necessary to prevent it from running out of available phone numbers. Eventually this was tabled; a technique called number pooling had delayed exhaustion of phone numbers in the area code.
The Kentucky PSC delayed action on a new area code several times, going so far as to suspend their intentions indefinitely [PDF] in 2010.
A brief history of 270
In 1999, Lockheed Martin (then the administrator of the North American Numbering Plan) published a memo [PDF] about the impending exhaustion of the 502 area code, which at the time covered the entire western portion of the state. A year later, area code 859 was created from area code 606, serving Lexington and northern Kentucky.
Split vs. overlay
When public meetings resumed regarding the implementation of area code 364, participants recommended an overlay as opposed to splitting 270. While an overlay allows everyone to keep their phone number, it also requires everyone to use ten digits to dial even local numbers. This was a point of protest among some users, but saves businesses money since they would not have to print new marketing materials.
The state of 364 today
According to NANPA, as of Sunday there have still been zero phone numbers assigned out of the 364 area code, 18 months after its introduction. It seems some of the hype in bringing area code 364 to western Kentucky was somewhat unfounded, but at least it is there for when 270 eventually does run out of available numbers.