"It was like any big conversion, except we weren't at the helm of it," Dick said. "We've performed a lot of mergers, so we're used to managing ourselves, but there's a level of confidence you have in yourself that you don't have in a vendor."

Scheuble suggests trying to get the vendor to time the transition to your benefit. For instance, when Spyder moved from its first ASP to Fortrust, the new provider timed the data center move to coincide with an upgrade that Spyder needed anyway, and then it ran the systems in parallel until Spyder was comfortable with the new setup.

"I was dealing with the same people, and even though the hardware had to be moved to their facility, it was well organized, so there were no problems," Smith said.

Richards also endured a data center move from Charlotte, N.C., to Gilbert, Ariz., but the new provider maintained the existing facility for a year and a half.

The most important thing for customers of acquired outsourcers to keep in mind, Scheuble said, is that they have a lot of room to negotiate. "They have more leverage than they think," he said. "If a company just went out and paid a premium for another company, it needs to retain those customers."