>(This dialog must be opened when Command-Shift-V is pressed)

According to Apple's [Pages Keyboard Shortcuts](http://www.apple.com/support/pages/shortcuts/body.html) support page, there is no command-shift-V nor shift-command-V, so if that exists, it is unpublished.

edit: I've been informed in the comments that it is an Insert menu item.

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Possibly helpful to you: 

to see the list of keyboard shortcuts in Pages, choose Help > Pages Keyboard Shortcuts.

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From the page linked above:

>Paste and match style of destination text..............Option-Shift-Command-V

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Also, try checking in System Preferences.app/Keyboard control panel/Keyboard short cuts for any conflicting shortcuts.

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[This may also be helpful to any experiencing inconsistent keyboard commands](http://www.youtube.com/watch?v=aTmOn_TXm24)