SmartGit/Hg 4.5 (and older) do not offer to start the git command line, however you may configure the 'Directory Tool' (Preferences, Tools) to open a terminal (or DOS box), so you can invoke the command line quickly.
Update: Since SmartGit/Hg 4.6, you can configure multiple Directory tools in the Preferences. After a fresh install (or after removing tools.xml
from SmartGit/Hg's settings directory), default tools will be created. If your git
executable is not on the path, an Open Git-Shell tool will be among them.