Explanation
A service relationship is defined as the cooperation between a service provider and service consumer. Service relationships are established between two or more organizations to co-create value. An organization can play the role of provider or consumer interchangeably, depending on the situation.
https://www.bmc.com/blogs/itil-key-concepts-service-management/#:~:text=and%20stakeholder%20managemen

Explanation
Service desks provide a variety of channels for access including:
Phone calls, which can include specialized technology, such as interactive voice response (IVR), conference calls, voice recognition, and others.
Service portals and mobile applications, supported by service and request catalogues, and knowledge bases.
Chat, through live chat and chatbots.
Email for logging and updating, and for follow-up surveys and confirmations.
Walk-in service desk (which are becoming more prevalent in some sectors, such as higher education, where there are high peaks of activity that demand physical presence)., Text and social media messaging, which are useful for notifications in case of major incidents and for contacting specific stakeholder groups, but can also be used to allow users to request support.
Public and corporate social media and discussion forums for contacting the service provider and for peer-to-peer support.
https://www.bmc.com/blogs/itil-service-desk/