VeriSign has agreed to buy m-Qube, which sells software and services for delivering digital content to mobile phones, for about US$250 million.

It's the latest move by VeriSign designed to help it build a business selling products and services that let companies distribute digital content via broadband and mobile networks. The company is best known today for security infrastructure products.

M-Qube sells a wireless gateway platform that allows companies to deliver video, chat services and other content to mobile phone users. It also manages mobile virtual storefronts and marketing campaigns. It has access to about 200 million cellular subscribers in North America through carrier relationships, according to VeriSign. Customers include Sony Pictures and Warner Music Group.

The acquisition helps build out VeriSign's content management and delivery platform aimed at carriers, Internet portals, media companies and consumer brands. It's the biggest of at least three acquisitions it has made in this area this year.

In February it said would buy 3united Mobile Solutions AG, an Austrian wireless applications service provider for €55 million. Then last week it said it would pay $62 million to buy Kontiki, a Mountain View, California, company that makes a digital video distribution system.