David Lubars, CEO and chief creative officer of BBDO West, said the loss isn't expected to result in any staff layoffs since the agency has picked up significant business from Best Western International, PepsiCo's Aquafina brand and Starbucks Coffee Co.
Executives close to the business said there may be internal squabbling between the two co-owners that is causing a change in or problems with the advertising direction.
"The partnership works very well," said a spokesman for L.A. Cellular.
He added that the review is in the "embryonic" stage, with L.A. Cellular just beginning to look at agencies.
He said he expects the selection process to take three to four months.
The new agency will face a challenge in the hotly contested market, with rapidly growing ad budgets from competitors including AirTouch, Nextel Communications, Pacific Bell Mobile Systems and Sprint PCS.
Mr. Lubars said he is proud of the work BBDO did; the agency won a Cannes Gold Lion in 1997 for its creative work for the brand.