Many GNOME 3 applications now use a selection mode design pattern, such as Documents, Boxes, Photos and Disks. This uses a checkmark button in the toolbar, which creates a selection mode.

Using a selection mode in contacts will be consistent with other applications, therefore. It also offers the opportunity to allow multi-select for deleting and to use the main contact list for linking. The latter is a big improvement, since it means that we don't have to worry about having a separate contact list elsewhere.

Mockup:

https://raw.github.com/gnome-design-team/gnome-mockups/master/contacts/png/selection-mode.png