Area code 813
Area code 813 covers all of Hillsborough County, the city of Oldsmar in Pinellas County, and the central portion of Pasco County. The eastern portion of Pasco County is in area code 352, while the western portion is in area code 727.
Area code 813 became Florida's second area code in 1953, when it was split from the state's original area code, area code 305. The area code stretched along the Gulf Coast from Pasco County to Collier County and included the cities of St. Petersburg, Sarasota, Fort Myers, and Lakeland.
Split into area codes 941 and 863 
Split into area code 727 
Although the 1996 split was intended to be a long-term solution, within only two years, 813 was close to exhaustion again due to the rapid growth of Tampa Bay area and the proliferation of cell phones and pagers. The Florida Public Service Commission decided to assign area code 727 as another area code for the region. It was originally supposed to be an overlay for the 813 territory. However, overlays were still a fairly new concept at the time, and the mixing of area codes in the same region, and the resulting requirement for 10-digit dialing, was met with considerable resistance.
With this in mind, on February 1, 1999, area code 727 became the new area code for most of Pinellas County (except Oldsmar) and western Pasco County, leaving the present area. Oldsmar, being right on the Pinellas/Hillsborough line, stayed in 813 despite being in Pinellas. Oldsmar's trunk was wired into the Tampa line and it would have cost too much for GTE (now part of Verizon), the dominant phone company in the Tampa Bay area, to rewire it. Another reason was that Oldsmar had most of the dialup Internet access numbers and alarm system reporting numbers in Tampa and St. Petersburg, since it was the only local exchange that was a local call to both cities. The cost of reprogramming thousands of alarm systems and replacing older units that couldn't handle ten digits was also a factor in the decision to keep Oldsmar in 813.
See also 
- "DEMAND FORCES SOUTHERN BELL TO MAKE A SWITCH IN AREA CODES" - The Orlando Sentinel, Sept. 1 1986
|Florida area codes: 239, 305, 321, 352, 386, 407, 561, 727, 754, 772, 786, 813, 850, 863, 904, 941, 954|
|West: 727||Area code 813||East: 863|