Facing the impending exhaustion of phone numbers in 10 of the state's 13 area codes by 1999, the California Public Utilities Commission has approved the use of area code overlays-but not until after number portability is introduced in California.

The decision, which paves the way for the eventual demise of area codes based on unique geographical areas, could also help usher in 10-digit dialing and location number portability, which would allow carriers to assign numbers without regard to where the end user lives within the state.

But until 1998 or 1999, when the system for statewide number portability is introduced, traditional geographic area code splits will be required, according to the PUC. The PUC also voted to split the 415 area code next year, a move that will create 7.9 million new numbers. The agency reiterated its stance that until Pacific Bell is granted special permission by the PUC to use an overlay, splits will continue to be California's way of dealing with its phone number crunch.

That requirement has Pacific Bell officials concerned. "The outcome of the commission's action prevents us from applying the overlay solution anywhere until we can secure approval from the PUC," said John Gueldner, Pacific Bell's vice president for regulation. "As it stands now, the availability of numbers in the 310, 619, 510 and 714 area codes is critically low, and we're concerned that we may run out of numbers before a geographical split can be implemented."

The overlay approach allows the carrier to introduce the new area codes more easily because there is no mandated permissive dialing phase as part of the new code's rollout, said Ron Brown, Pacific Bell's area code relief planner for northern California. "Over the long run, we have lower expansion to accommodate within our internal systems," said Brown. "That makes it less expensive, and by skipping the permissive dialing phase, we can put the new codes in place sooner."

The PUC reversed its earlier position against overlays, a stance it had adopted because of fears that the overlays would give unfair advantage to incumbent Pacific Bell over new competitors. The fear was that consumers would be reluctant to purchase service from new entries into the market if it required them to change to a new area code

But with portability and the advent of 10-digit calling to and from any spot in the state, the need to regulate area code splits will vanish, and customers will be able to take their phone numbers with them anywhere they live.

"Essentially, even though splits have been preferred in the past, we're moving toward a time when area codes will have nothing to do with geography," said PUC regulatory analyst Natalie Billingsley.

But the technology for portability is still not expected to arrive until 1998, meaning that Pacific Bell could be forced to split area codes even with the ruling.