Sure has completed its takeover of Airtel Vodafone.
The deal was approved by both Jersey and Guernsey's authorities.
Sure says it signals a £48 million investment in a 5G mobile network, and that islanders will benefit from faster speeds and greater coverage.
Sure Group CEO Alistair Beak called it an 'exciting day' for the future of Channel Islands telecommunications:
“We want existing and new customers to know that the large investment we’re making will lead to significant improvements to their connectivity, speeds and coverage, as well as value for money through innovative products and services.
"The new mobile network, complemented by our extensive fibre network, will mean we can stay ahead of future demand driven by our increasingly digital lifestyles.”
Airtel Vodafone staff have joined Sure.
As part of receiving permissions, Sure has committed to allowing Airtel Vodafone customers to continue on their existing plans for up to three years.
Initially, the two will continue two companies will continue to operate separately.
Sure has also made a deal with the CI Coop, which will launch Coop Mobile offering its own mobile services and pricing over Sure's network infrastructure to 'preserve competition and customer choice'.

Haut Du Mont trial: Worker told colleague he 'didn't test' gas main
Shear relief for Romerils as Shaun the Sheep found!
Electricity companies sign four-year deal with EDF
Filming underway for Bergerac Series 3
Teenagers wanted to join Jersey Youth Assembly
Jersey Bulls knocked out of FA Cup
Residence and employment rules simplified
RNLI Jersey back on Saving Lives at Sea