Wireframes can be part of the UCD phase or they can be delivered as a separate phase. Hamilton Buchanan separates wireframes into two distinct categories. 1) Process wireframes (showing the process required for a particular task i.e. newsletter subscription and 2) Structure wireframes which indicate the formal structure of the site.
Structure wireframes are linked to a sitemap and focus on content placement and navigation on pages. It takes longer to develop structural wireframes than process, as the Information Architect develops them from the sitemap and functional specification / requirements documentation, whereas processes, by definition, are usually closely defined. Process wireframes are functions of the site and have their own diagrams. These diagrams show conditional process flows. As an example, a simple process like a newsletter subscription can have up to 5 pages (subscription page, error page, success page, unsubscribe page, confirmation page) and may be completed in a few hours. However, e-commerce functionality may be much more complex and time consuming.
Wireframing quotations are based on the number of either 1) Structure or 2) Process wireframes required for the site.