This ends weeks of speculation that followed the mobile network's decision to move its business out of the incumbent, WCRS, earlier this year.
The pitch is being handled by ISBA. A decision is expected in May. Media planning and buying, which MindShare handles, is not affected.
The mobile network's advertising rethink follows the signing of John Penberthy-Smith as the marketing director in January. He said: "We are looking for teams that can deliver great creative work and provide leadership across a range of media. The agencies we've shortlisted all have a young and challenging outlook, and offer truly integrated communications support."
In what is seen as a significant shift away from the big brand campaigns that featured heavily last year, 3 is expected to channel a large proportion of its marketing budget into direct activity to support the expansion of its retail store network. TV ads are not expected to run until the second half of the year.
During its three-year tenure on the 3 account, WCRS produced some of the most memorable advertising seen in recent years. TV ads included elements such as musical jellyfish, a singing cherry and housewives with glowing orbs.