United Airlines loves its 23,000 iPhone 6 Plus phones so much, it's buying 6,000 more

United Airlines on Tuesday announced that it's buying more than 6,000 iPhone 6 Plus phones for its customer service employees.

This is on top of the 23,000 iPhone 6 Plus phones it bought for its flight attendants a year ago.

United has written custom iOS apps for the phones that will do some pretty nifty things.

For instance, the app will let a customer service rep print boarding passes or tag baggage from anywhere in the airport, as long as the customer has already checked into the flight.

Or they can help passengers find alternative flight options, and such.

United has been an all-in poster child for Apple since 2011, when it outfitted its pilots with 11,000 iPads.

Apple's success with United is important to the company. It is really trying to push its devices more deeply into the lucrative commercial/business markets, first through its partnership with Apple and more recently with Cisco.

CEO Tim Cook sees sales to businesses as one of Apple's big growth areas.

And, he says that this push is working. He said in October that sales to large enterprise companies "accounted for about $25 billion in annual Apple revenue in the last 12 months, up 40% over the prior year and they represent a major growth vector for the future."