UPDATE 1-Vodafone signs Warner music deal

* Deal gives Vodafone access to all four majors

* Music will be DRM-free

LONDON, Sept 21 (Reuters) - Vodafone (VOD.L) has signed a deal with Warner Music Group WMG.N which will allow the world's largest mobile phone firm by revenue to offer music without anti-piracy software from all four major labels.

Vodafone said on Monday the deal would make it the first global mobile network operator to offer over-the-air access to music from the four majors. It had previously signed deals with EMI Group, Universal Music (VIV.PA) and Sony Music.

The Warner music from artists such as James Blunt will be without anti-piracy software, or DRM-free, which means it can be played on any device including iPods.

"The response to the DRM-free offering in all the markets where it has launched has been incredibly enthusiastic," said Pieter Knook, Vodafone Internet Services Director. "Our customers love ... the flexibility that DRM-free on mobile gives them."

Music companies are desperate to sign new digital deals as online piracy eats into traditional revenues, while mobile groups are also looking to diversify and increase customer loyalty through new services. (Reporting by Kate Holton; Editing by Dan Lalor)