A Service Desk is a primary IT service called for in IT service management (ITSM) as defined by the Information Technology Infrastructure Library (ITIL). It is intended to provide a Single Point of Contact ("SPOC") to meet the communication needs of both Users and IT employees. But also to satisfy both Customer and IT Provider objectives. "User" refers to the actual user of the service, while "Customer" refers to the entity that is paying for service.
A nice service management software you can check: iKode service desk
http://www.service-management-software.org/

We have found that "Service Desk" is a customer friendly wrapper for things like Incident Management, Request Fulfillment, and various other smaller functions handled by the samepersonnel. In this sense, it might be best thought of as a service offering that packages together a number of more specific process based services.

Because it is a supports most or all other services in the environment, it is also a *shared* service, and therefore might best be included as a component of other core services. This allows the costs of running your service desk to be fairly distributed among the various core services that it supports.

For example, if an ERP service generates a disproportionate # of incidents, that typically means more time is spent supporting it, and it should carry a higher portion of the overall costs of the service desk organization than a more consistently performing service that generates fewer incidents.

Very often we seem to be stuck with labels and what things should be called.

The important thing is that what ever it may be called (service or function) is not as important as what the role of the service desk in terms of the end customer and what are the services that the desk provides to them.

Most service desks provide services which terminate with their staff. What is popularly called a first time resolution or first time fix.

Typically they provide this service across multiple services. For example they may take and resolve calls on Email Services, Active Directory Services, Desktop Software services etc.,

In this avatar they are indeed service providers and therefore responsible for processes that they operate to provide these services.

Where they are unable to resolve (due to either technical or security related issues) they route the ticket to the appropriate group.

Here their responsibilities are more in the nature of Appropriate Classification, Accurate Problem Description Recording and Routing to the group which is most likely to provide a technical resolution.

This is probably why there is confusion about whether they provide a service or a function?, do they need SLA? Ofcourse, if they are providing first line of support to a customer for Email, then the SLA for Email services certainly should apply to them.

I think the trick is to see the service desk as part of the entire IT Supply Chain required to provide any given service.

I belief it is a function that enables you as an IT department to understand where your customers are having problems and allows you to manage customers queries and issues through a well planned and managed process.
Thinking of the Service Desk as a service invariably leads to a barrier to service rather than amazing entry point for us to know and understand how users experience our IT Service.

The Service Desk and its staff are a 'function' according to ITIL v3. The services the function provides are classic ITIL services. The delivered services are usually provided under Service Level Agreements (SLAs) with the customer.

For example, your service desk (function) might provide three levels of support service: 5 days x 8 hours, 6 days x 12 hours and 7 days x 24 hours. The SLAs will define what services (activities) will be provided by the function, what the required (and agreed to) "response" times are for each level of service and what the "cost" or "charge" is for each level.

The provided "Services" might be defined as; logging an Incident for the user, submitting RFCs requested by the user to Change Management, providing 1st level Incident resolution support, assisting with requests for information, access, new user start-up (laptop, approved software and initial user training), etc.

Incident Management is not a service, but providing 1st.level incident phone or web support would be. Consider a "call center" that only logs calls and forwards them to the appropriate resource for handling. This desk is not providing a1st level incident response service, only a "call logging" service.

Interesting as I am having the same debate with a client I am working with (I am a consultant).

They instinctively want to call Service Desk a service, but I am trying to discourage it. To me, Incident Management is only one of the many processes done by IT in the delivery of the services. And we aren't describing any of the other functional units of IT (e.g. ops, app support etc) as 'services' so why should we for Service Desk?

The point that I think seemed to resonate was when I asked 'so will you have a SLA for service desk, like you do for email, desktop, ERP, blackberry etc? Who with? And will you re-bill/invoice someone purely for the service desk service?' The answers were 'no'. There will be SLAs for email, desktop etc. The SLAs will include incident response times, target resolution times etc (and are in fact standard across all services). The cost of service desk will be apportioned as part of the cost of the 'real' services, just as network, storage, management will be etc.

Another test I sometimes use (to test if something is a service) is "if it was the only service you offered, would it make sense?". For an internal IT dept, if it only offered service desk, it would not make any sense - the service desk only offers value in the context of supporting IT Services.

But I dont suppose there is a right or wrong answer and it depends on your perspective. If your organisation is a provider of outsourced IT services, then yes 'service desk' can be a service you sell.