The roll-out has begun. Earlier this month Google said it would be adding ad group-level mobile bid adjustments to enhanced campaigns. As of yesterday, ad group mobile bid adjustments are available through the AdWords API.
The addition of ad group-level mobile bids will allow advertisers to have more granular control within their campaigns. Until now mobile bids could only be set and adjusted at the campaign level in enhanced campaigns.
Ad group-level mobile bid adjustments will eventually be available within the AdWords Web UI and Editor, but specific dates have not been released.
Reminder: All AdWords “legacy” campaigns will be converted to enhanced campaigns starting July 22, 2013.