Looking to increase sales beyond its books-and-mortars stores, Barnes & Noble has signed an agreement with the mobile commerce service provider Digby to sell books, CDs and DVDs on BlackBerry-compatible devices. Under the deal, B&N is the exclusive merchant for books, music and DVDs through the Digby storefront, which is available as a free download at www.digby.com. BlackBerry users that click on books will see several hundred titles, mostly new releases and bestsellers, and the full B&N title database is also accessible. Sale terms are the same as on B&N.com, although a spokesperson said the system can’t currently accept membership discounts or coupons. B&N doesn’t expect mobile devices to generate significant sales initially, but the retailer sees the deal as a way to get involved with the expanding mobile commerce channel.