Amra already handles national sales for Trinity Mirror's regional websites and newspapers.
At Amra, mobile sponsorship sales will be led by associate director Paul House.
Rick Gleave, head of mobile, Trinity Mirror, said the company is now "heavily focused" on expanding its mobile services after spending 10 months "developing and building" the sites.
Regional sponsorship for Trinity Mirror's mobile sites will continue to be sold by its individual regional sales teams. Display and banner ads for the Trinity Mirror mobile sites are handled by Nokia.
The relationship between Trinity Mirror and Nokia is not affected by recent reports of 30 redundancies at Nokia's mobile sales house.