In a statement, D'Ambrosio said there are "substantial opportunities for Avaya" as large companies purchase next-generation communications systems.

Peterson could not be reached for comment, although analysts and some customers said they thought he had effectively run the company for six years. "Under Don, Avaya did a great job of creating a strong brand after being spun out of Lucent," said Zeus Kerravala, an analyst at Yankee Group Research Inc. in Boston. "Basically, the leadership change is good as we embark on this new dawn of [voice over IP] as software."

Kathy Brooks, president of the Atlanta Avaya Technology Users Group, said she had not heard of the executive transition and was not concerned about it. "I think Avaya is great and has done a great job for my company, has great service reps, and all my associations have been very positive," Brooks said. Her organization, which has 100 members, meets about six times a year.

Brooks is an IT manager at ACS Government Healthcare Solutions in Atlanta, where about 2,000 users have Avaya IP phones and IP networks from Avaya.

Christine Olsen, president of the Avaya users group in Buffalo, N.Y., said members in her group use Avaya equipment purchased through integrators and resellers, which have limited direct involvement with the company. "Most of us are satisfied with Avaya equipment, but Buffalo is a smaller market, and Avaya has chosen not to service us directly," she said.