Ring-back tones will become the single largest source of mobile entertainment revenues within two years, experts predict.

IDC said that the number of worldwide wireless subscribers and customers will grow by more than a billion over the next four years, generating $800bn in global wireless service revenues by 2011.

The analyst firm expects mobile entertainment to account for 5.1 per cent of this total and 23 per cent of all mobile data revenues.

The vast majority of the revenue will be from ring-tones, ring-back tones and mobile television and video services.

IDC identified significant regional differences, but said that worldwide revenue and subscriber and customer totals are poised to increase at least 25 per cent annually between 2006 and 2011.

The analyst firm predicts that ring-back tones will overtake ring-tones in 2010 and become the single largest revenue source for mobile entertainment due to a variety of "inherent" advantages.

"The fact that ring-back tones is expected to increase its share several percentage points through the forecast period is a testament to the inherent strengths of the service," said Lewis Ward, research manager for wireless communications research at IDC.

"One could argue that because ring-back tones is the most closely tied into the network, and cannibalisation from third parties is virtually impossible, it has some additional advantages over other mobile entertainment services and content types for mobile network operators."