Google allows 3rd parties to write apps that do this using the Contact API.
There's a list of such 3rd party apps that plug-in to Google Apps in the Google Apps Marketplace, along with a ton of other useful add-ons such as CRM, project management etc
At Cloud Logic, we tend to recommend Floreysoft Shared Groups. Basically, this allows you to share any of your Contact groups in Google Apps with other people in the company and to let them have read-only access or edit ability. Once shared, the groups appears in their own Contacts and therefore can be synced to their smartphone (and Outlook if they're syncing that with Google Apps). And of course all the email addresses in the shared group will work in auto-complete when they start typing it in the To field in an email.