"We will continue to provide a full spectrum of mobile services to Virgin Media and support Virgin Mobile customers under our existing MVNO agreement, until they transition", it said.
"Twenty years ago Virgin Mobile became the world's first virtual operator and this new agreement builds on that heritage", said Lutz Schüler, Virgin Media CEO.
Because of the deep MVNO infrastructure, customers should experience limited disruption and won't even need to change their SIM cards.
Virgin wanted significantly higher data allowance growth, requiring more investment, and 5G from the start of the contract, which would have eroded BT's technological advantage, the source said.
Virgin Media is ditching telecoms group BT and switching its three million mobile phone customers to the network run by Vodafone.
According to a report in the FT, the loss of Virgin Media's business will leave a £200m pa hole in BT's income stream. "It will open up a whole new world of opportunity for Virgin Media as we focus on becoming the most recommended brand for customers". "We've worked with BT to provide mobile services for many years and will continue to work together in a number of areas".
The British cable TV and broadband company, owned by USA group Liberty Global, pioneered the mobile virtual network operator (MVNO) model, when a company offers own-branded mobile services on an established partner's network.
Virgin said it would offer 5G on Vodafone's network earlier than the transition of existing services.
Virgin Media, which offers cable TV and broadband services, pioneered the mobile virtual network operator (MVNO) model, whereby a company offers own-branded mobile on an established partner's network.
Analyst Paolo Pescatore, from PP Foresight, said: "For Vodafone, this is a great coup as it continues to turn around its fortunes in the highly competitive United Kingdom market".
It is understood that the United Kingdom was never a market under consideration, but former Vodafone Group CEO Vittorio Colao refused to rule out future talks. For years, Virgin Media has been hampered with its current EE deal.