National Australia Bank is cutting the number of business bankers on its payroll and steering customers towards call centres for help instead.Over the last week, customers of NAB have received letters signed by Cindy Batchelor, the bank's head of small business banking, advising them of the change."Instead of one banker, you now have a team of small business specialists who can help advise you," Batchelor wrote.The decision reverses a long-standing facet of NAB's business model in business banking in Australia.Bank management used to argue that it employed a distinctive service model in business banking and would make a virtue of recruitment drives to increase the number of specialists.Paul Dowling, principal analyst at East & Partners, said: "The issue for NAB and the other big three really is the cost of service delivery."They are all confronting slack credit growth, to put it mildly. There is very little cross-sell. The business appetite for new products is waning."It's all sentiment driven."There are other indicators of a shift in NAB's approach to the business market.While growing, NAB's share of credit to business (provided by banks) is now doing so at below system.  Over the six months to April 2012, NAB reported growth of 2.8 per cent compared with 3.9 per cent for all banks.NAB had reported growth well above system in six months prior to this, which now looks like the end of an extended period of market share growth.