The 812 area code that spans most of the southern half of Indiana is on pace to use up its remaining numbers by late 2013, making it the next area code state regulators could split up.

An April report to the Indiana Utility Regulatory Commission shows that the area code has exhausted 91 percent of its prefixes — the three numbers after 812 — and the rest will be assigned by the third quarter of 2013, IURC spokeswoman Danielle McGrath said Wednesday.

The panel can take no action to address the dwindling numbers until the North American Numbering Plan Administrator, an independent body, files a petition with the IURC on behalf of the telecommunications industry.

When that request is made, McGrath said the IURC will investigate and "determine what options best fit the affected area."

She said those options include shrinking the geographic area currently covered by 812 and adding a new area code or codes for the rest of that district. Or, the panel could allow existing numbers to remain unchanged but require new numbers to carry a different area code.

Such an "overlay" would mean some residents would have to dial an area code to call even their neighbors.

The same trends that are eating up numbers nationwide are shrinking the 812 prefixes, chief among them the proliferation of cell phones.

Michelle Gilbert, a spokeswoman for Verizon Wireless in Indiana, said that growth is being fueled in part by parents buying cell phones for their children at earlier ages.

"If there's a family of four, all four might have cell phones, whereas families used to have a single telephone number," she said.

The growing popularity of wireless cards for laptops that link consumers to the Internet is also taking up telephone numbers, although many people don't realize those modems are assigned telephone numbers, Gilbert said.

She herself uses four different numbers — her personal cell phone, her work cell phone, her Blackberry and an air card for her work laptop.

When the day comes for a change in the 812 area code, small businesses affected by new area codes would face a financial burden because they would have to update business cards, brochures or their signs with their new numbers, said Angie Satterfield, coordinator for retail projects for Switzerland County Tourism in southeastern Indiana.

Satterfield, who lives in the Ohio River city of Vevay, said that an area code shift would also rile some residents in the 812 region that encompasses the cities of Bloomington, Evansville and Terre Haute.

"We have businesses that have been here for generations and everyone knows their phone number by heart. Suddenly changing them, that's felt — and not just economically. It's sort of a little disconcerting to people," she said. "You know, change isn't always embraced."

The state's five other area codes are currently at least several years, or up to a quarter-century, away from running out of prefixes.

Those area codes and the projected year when their prefixes will be exhausted are: 317 (2017), 765 (2018), 219 (2031), 260 (2034) and 574 (2036).