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In more bad news for AT&T, a Jan. 13 study from ChangeWave is the latest to suggest that the original Apple iPhone provider may suffer a customer exodus once Verizon begins selling its own long-awaited iPhone Feb. 10.

Days before Verizon’s big Jan. 11 announcement  — “We are pleased to introduce millions of wireless users to the industry-leading iPhone 4 on the nation’s most reliable network,” Verizon COO Lowell McAdam said in a statement — ChangeWave asked 4,000-plus consumers how likely they were to switch providers in the next 90 days.

Fifteen percent of both AT&T and T-Mobile customers said they were “very/somewhat likely” to make a switch, while only 4 percent of Verizon customers said the same.

Wading into the figures, ChangeWave found AT&T’s 15 percent to represent its highest churn rate in the past 18 months of polling, more than doubling the 6 percent who answered similarly in June 2009 and nearly also the 8 percent who said the same in June 2010.

Behind their “weakening loyalty,” reports ChangeWave, is a general displeasure with the service, with 42 percent citing poor reception/coverage as their reason for considering leaving, and 27 percent citing dropped calls. (Another 17 percent said cost was the motivator.)

When ChangeWave directly asked AT&T customers whether they planned to switch to Verizon “if-and-when they begin offering the iPhone,” 60 percent said no, 16 percent said yes and 23 percent weren’t sure.

For more, read the eWeek article: Verizon iPhone to Have ‘Major Impact’ on US Providers: ChangeWave.