From the Nokia press release:
During the address, Mr. Kallasvuo also highlighted the Nokia 5800 Xpress Music devices as a great success: "Consumer response has been well beyond expectations, and it has the potential to become our most successful device ever. We estimate that this smartphone alone accounts for around 20 per cent of all touch screen devices sold worldwide. It offers unique value for those who want to experience their music on the move, particularly when combined with our innovative Comes With Music service."
Update: As noted in the comments, the figure of 20% marketshare refers to sales in Q1 2009 only.