ST. LOUIS — Customer-management software maker Amdocs said today it agreed to buy Qpass, a Seattle-based provider of digital commerce software, for about $275 million in cash.

Qpass, a private company, makes software that processes sales of digital content for wireless carriers. Applications include service activation, billing, product management, marketing, customer service and third-party incorporation.

Qpass has annual sales of $42 million and employs more than 300 people at offices in Seattle, London and Vienna. The company has relationships with more than 300 content providers, including Cingular, Sprint and T-Mobile, Amdocs said. Amdocs said it bought Qpass to take advantage of the transformation of wireless companies from voice carriers to providers of a range of personalized services and digital content.

Amdocs expects the transaction to close in the third quarter ending June 30.