The "bolt on" promotion offers subscribers a chance to purchase extra text messages and calls at competitive rates in addition to their existing mobile packages.
The campaign, created by Vallance Carruthers Coleman Priest, features seven special builds with giant bolts built into them. The bolts are made of wood and vinyl to create a metallic look.
The posters, which are placed across London, form part of a larger strategy, incorporating TV, radio and national press ads.
Media buying for the campaign was by PHD through the outdoor specialist Outdoor Connection. The posters were written and art directed by Rooney Carruthers. JCDecaux, which owns the seven hoardings, worked with O2 to create the campaign.
Tom Sutton, the media manager at O2, said: "'Bolt ons' are great value extras to add to your O2 mobile package. O2 wanted to simplify the communication of the proposition and to ensure good standout. JCDecaux worked with us to illustrate the 'bolt on' concept by adapting its 48-sheets to create a visual solution that exactly matches our requirements."