A software-based distributed architecture allows rapid provisioning and flexible management of fault-tolerant call centers for interaction between companies' agents and outside customers via multi-media messages, using both real time and non-real time messages. The real time messages include web-based chat, forms and applications sharing, PSTN calls, and incoming and outgoing Voice over IP calls. The non-real time messages include web call-back requests, voice messages, fax messages, and email messages. The architecture provides for sharing of non-dedicated resources among multiple companies, mirrored hot backup, dynamic resource provisioning and allocation, dynamic load balancing, and implementation of service controls on individual companies in accordance with subscription service limits.