There is no such thing as an internal customer.
I developed this edict long before user experience, or even User-centered design were things. There was however, total quality management (TQM).
One of the key aspects of TQM was a focus on ensuring that you provided quality work to your “customers”. The adoption of TQM lead to a bit of a dilemma for folks who didn’t deal directly with an organization’s real actual customers. Folks like IT developers and analysts. Thus was born the concept of the internal customer. If you are writing requirements; your customer is the developer and tester community.
The problem with this is that is doesn’t necessarily lead to the best experience for real customers. Providing good customer service to the next person down the stream can easily mean making their job easier at the expense of the end user (customer).
So let’s define what a real customer is. A real customer uses your organizations goods or services. In most cases a real customer give your organization money or something else of value for the privilige of doing so.
There are still remnants of TQM out there, but it’s no longer much of a movement. However, there is still the temptation to define your own worth in terms of these internal customers. Don’t do it, whether it’s someone in your organization; your client; or anyone else who isn’t a real customer. It’s a trap. In order to achieve a focus on your customers you have to make sure that everyone in your organization understands their job in terms of how it relates to your real customers, not your imaginary internal ones.