Google announced that ad group-level mobile bid adjustments will start rolling out today and continue over the next couple of weeks in the Web UI. The added feature went live in the AdWords API last week.
Like the elusive Keyword Planner that is rolling out now, ad group mobile bid adjustments are only available in a small number of accounts today. So, be patient and remember it could take two weeks or so to be active in your account.
Google made the announcement along with the introduction of the ‘Set bid adjustment’ button to make bulk edits to location and daypart bid adjustments.