Rostered agencies would handle specialist contracts - such as promoting product or service launches, music or gaming initiatives - for the challenger brand.
The creation of the roster would not threaten Lexis PR's hold on the firm's core consumer business, insisted UK head of consumer PR Elaine Quinn, who is spearheading the project.
She said Lexis was making a 'really good' fist of promoting 3 but that 'from time to time we could supplement this with a project-based approach'.
Quinn added that she had thus far merely had 'initial discussions' with undisclosed agencies, and that a roster of preferred suppliers with no guarantee of work was the likely outcome of the talks. She stressed that plans were yet to be finalised.
Agencies that 'understand the needs of challenger brands' are being approached, with decisions due in the 'coming weeks'.
The overall aim of project briefs would be to echo Lexis's ongoing theme of positioning 3 as 'fun and different' to competing mobile networks, with agencies needing to 'see the potential of 3 technology and explain it', added Quinn.
3's consumer-side plans emerged following news last week that the firm is also reviewing its public affairs agency support, with Lexington Communications the incumbent agency (PRWeek, 24 June).
After a well-chronicled difficult start, 3 - a UK subsidiary of Hong Kong-based Hutchison Whampoa - now has more than three million subscribers.
It has built up its customer base largely by offering cheaper voice calls than rival networks.