Having enrolled 130,000 customers for its biometric voice authentication system, which can identify callers by the sound of their voices, National Australia Bank is now considering exploring "mood monitoring" - using technology to bump angry customers up the call centre queue.Speaking at the Voice Leadership Forum in Sydney yesterday, Tim Andrew, general manager for ATMs and self-service at NAB, explained that interactive voice recognition systems could potentially be used to route incoming calls based on the "mood" of the voice. Someone with an angry voice could be bumped up the call centre queue and dealt with ahead of other more genial callers to avoid making a bad situation worse.Andrew said that since announcing the voice biometric initiative, in 2009, 130,000 NAB customers had enrolled for the programme. This is still well shy of the two million people the bank would like to enrol in the initiative, which is intended to provide streamlined, but secure, access for callers.He said the bank was currently reviewing the biometric enrolment process. He said that while customers who were inclined to use self-service banking were more likely to self-enrol in the voice biometric scheme other customers might more sensibly be recruited to the programme during the "on boarding" process. This is when they first sign up for online or telephone banking. At this stage they could be offered the option to enrol and have their voice captured while in their branch.NAB is also considering how it might  integrate voice biometrics with other services - mobile access, for example. "The mobile device is a place of congruence for internet banking and telephone banking. Can you have a voiceprint on a mobile for authentication?" he asked.Andrew said that, at present, NAB deals with 45 million calls a year, which come into the bank through 500 different numbers. While 30 million of these calls go directly to telephone banking, 15 million are distributed to the bank's 32 call centres, which employ the equivalent of 2400 full-time employees (call centres are often manned by part-timers). Five million of these calls are currently routed by speech commands.Using biometrics to authenticate a caller, coupled with voice recognition systems, can significantly boost the efficiency of contact centres - and also improve the customer's experience.NAB is a pioneer among the Big Four banks in the use of voice biometrics. Westpac, however, continues to examine the technology. Sam Jackel, who was formerly in charge of NAB's call centre programme, moved  last year from Melbourne to Sydney to take over as Westpac's project director for the bank's contact centre transformation project. Westpac is using voice recognition to route callers through the contact centre, and Jackel yesterday acknowledged that: "A technology such as voice biometrics lends itself well  [to contact centre application]." Like NAB, Westpac is wondering how it might securely enrol customers for a voice biometric project. Jackel acknowledged that the weakest point in the chain was the point of enrolment, where it was essential to know that the person whose voice was being recorded