IP Centrex faces the same challenge that managed services for traditional data face: a combination of mistrust on the part of the end user and lack of sales ability on the part of the service provider.As Joanie Wexler and Steve have been discussing in the Network World WAN newsletter for the past couple of weeks, managed services have historically had a hard time making a significant impact on the data side of the house. However, in spite of these limitations, the services actually make a lot of sense for many enterprises.The reasons for this lack of impact are multifaceted, but many of them come down to the simple fact that most enterprises are accustomed to providing their own services, because the requisite services were not available from the service providers. Consequently, after at least a couple of decades, a BYOB (Be Your Own Bell) attitude now pervades this marketplace. And the service providers have not helped this situation.On the one hand, service providers now offer excellent services for both data and voice. IP Centrex is just one of these options. But the service providers still have not been overwhelmingly successful at selling the services. And this comes down to the sales force.For IP Centrex to have a significant impact, the service providers will have to break the mold and show the same aggressive attitude that has dominated both the data communications and PBX industries over the years. Rather than hiding behind the \u201cwe\u2019re safe because we\u2019re The Phone Company\u201d attitude, both the technical and business benefits of the services must be articulated clearly.Admittedly, this is a tall order. But if IP Centrex services are not a success, the service providers have nobody to blame but themselves.