You've spent months carefully vetting agencies to ensure you choose a partner with no client conflicts. After a lengthy process, one shop rises above the rest. You've had "chemistry check" meetings and determine that culturally, you and the agency are a perfect fit.

Then, it flips. The agency you handpicked has merged with another shop without telling you. You now have a conflict on your hands.

That's just what happened to Volvo last week. The carmaker is weighing whether it should launch a digital-agency review in the wake of the merger of its lead shop, LBi, with Digitas, which works with rival automaker General Motors. The combination happened without warning to Volvo's global VP-marketing, Richard Monturo, who read the news on Ad Age's website.

In a business where service and relationships are paramount, such a misstep calls for a rereading of Communications 101. But such incidents are becoming far more frequent in adland -- and they cut both ways.

Agencies these days often learn about cracks in their client relationships via phone calls from reporters, or discover that their accounts are going into review from media reports.

Publicis Groupe executives -- including CEO Maurice Levy -- were famously blindsided to learn that GM's former CMO, Joel Ewanick, had shifted the entire Chevy creative account to Goodby, Silverstein & Partners without ever getting a phone call.

It all spells a troubling breakdown in communications between clients and agencies. Some say sound account management -- the domain of the Ken Cosgroves and Pete Campbells during "Mad Men" days -- is being lost in the accelerating speed of business. But it doesn't help that clients and agencies have more partners than ever. There are multiple points of contact, making for a spiderweb of communications.

The relationships are also shorter and more fragile. According to Atlanta search consultancy The Bedford Group, in 1984, the average client-agency relationship tenure was 7.2 years. By 1997, that number fell 25% to 5.3 years. Today the average client-agency tenure is thought to be less than three years. "As an industry, it feels like we have lost sight of what it means to have a relationship," said Elizabeth Zea, partner at Juel Consulting. "I see three things that really get in the way. "Time, technology and trust."

Agency executives and clients alike have never been so time constrained or asked to do so much with so little. "Technology isn't helping," she noted, adding that there's a "Why talk when you can text?" mentality that's permeating the business world.

"It feels like conversations are more frequent, but less substantial," Ms. Zea said. "And none of this bodes well for trust."

In Ms. Zea's experience, the more preparation the better. She once saw a 10-page deck that organized the communications of how one person was being promoted within an agency, complete with chart after chart explaining who was responsible for making phone calls to clients.

It sounds extreme, but it works.

A good start on both sides? Appoint someone whose responsibility is to ensure that the communications plan of a big executive departure or hire, a merger or acquisition or the dismissal of an agency partner is done in a way that's professional and respectful to all parties.