Sally Beamand, senior PR and campaigning manager at 02, has replaced Hart at the mobile giant. 02 is among the initial client roster at Missive, which said it is establishing a partnership with a US-based PR agency to offer clients reach into the North American market.
Another initial client is Silicon Valley-based Trunomi, which develops mobile-based tech products for financial services providers and its own customers for online identity purposes. Missive is handling its introduction to the UK.
Hart and Koronka first worked together at Hotwire, the technology-focused PR agency, almost a decade ago.
Koronka left her position at Hotwire as head of financial services and tech almost two years ago to act as an independent comms consultant in the financial services and technology industries. Most recently she was the UK comms manager for Silicon Valley Bank.
Hart departed from 02 at the start of this year after almost seven years with the company. This included two years in her most recent role, where she led a team of 10 and was responsible for consumer, business and corporate PR.
Koronka said: "Missive is launching at an exciting time. The UK is home to an increasingly vibrant technology industry and we feel excited by the opportunity this presents to both Missive and our prospective clients."
Hart said: "Through the creation of Missive, Nicola and I bring together highly complementary industry backgrounds. Our specialism spans the breadth of the technology industry - for which we have a joint passion - and are fuelled by the combination of a decade of both in-house and agency experience."
Nicola Green, director of comms and reputation at Telefónica UK, 02's parent company, said: "It’s always sad to see members of your team leave but I am very proud that Emma has taken the brave move to start her own agency. I wish her all the very best for the future and look forward to working with Emma’s new agency, Missive.