Daniel Moth has additional copy support for his Windows Phone 7 app.
Source: The Moth
Some Windows Phone 7 owners already have the NoDo update, and others are getting it soon. This update brings, among other things, copy & paste support for text boxes. The user taps on a piece of text (and can drag in either direction to select more/less words), a popup icon appears that when tapped copies the text to the clipboard, and then at any app that shows the soft input panel there is an icon option to paste the copied text into the associated textbox. For more read this 'how to'. Note that there is no programmatic access to the clipboard, only the end user experience I just summarized, so there is nothing you need to do for your app's textboxes to support copy & paste: it just works.