A web-based hosted solution (a managed service or system) through which business entities create and manage communications campaigns, such as interactive campaigns that afford target recipients an opportunity to be connected to a contact center. The managed service carries out a communications campaign on behalf of a client. A “campaign” refers to a series of calls to a contact list using one or more sub-campaigns. A sub-campaign associates a list of contacts, a script, and a timeframe. An “agent” typically is a contact center operator. A “skill group” is a set of agents that are trained to handle a given script. Call pacing enhancements are implemented to allow simultaneous progress on multiple sub-campaigns under a skill group. The techniques enable control over the pacing of individual sub-campaigns when multiple sub-campaigns are running under a single skill group. The service also provides a framework by which a set of “pluggable” pacing models are provisioned and managed, preferably on a per-model basis.