Plain and simple, north Florida is running out of 904 phone numbers, so in the near future it may get a new area code.
The Florida Public Service Commission has received a proposal to create a new area code in the Jacksonville area. The FPSC says the 904 could run out of available numbers by 2024. But instead of splitting up the region the new area code would be what they call an "overlay"; that's a new area code be added to the same territory covered by the 904 area code, with new customers receiving the new code.
The proposal asks the Commission to make a decision about the additional area code by July 31. If approved, the changes would be carried out over a 13-month period.
I'm old enough to remember when Florida only had 904 and 305. but that's for another time!