Service Level Management (SLM) plays a central role to ensure the quality of service (QoS) in Public Cloud environments and requires a structured E2E approach to support the migration of critical services and sensitive data. In fact, the shift of responsibility to the Cloud Service Providers (CSPs) enables the customers (CSCs) to be more focused on the business, but, at the same time, they lose direct control on the actual QoS. This paper presents a conceptual SLM-as-a-Service framework, acting as proxy-based control point between consumers and CSPs, to manage the entire lifecycle of business services running on distributed and multi-vendor Public Cloud environments. A case study application in a global telco provider demonstrates the feasibility and effectiveness of the proposed solution.