Onecom has acquired the entire fixed-line and broadband customer base of True Telecom (which is in administration).
The deal sees 3,000 customers migrating to Onecom.
Onecom CEO Darren Ridge said: "This deal ends a period of uncertainty for True Telecom customers, while delivering a significant volume of fixed-line and broadband accounts to our business."
Onecom is based in Whiteley, Hampshire and has offices throughout the UK, including Northern Ireland.
It's on track to achieve £100m of turnover as it continues to grow through a combination of organic growth and strategic acquisition.
Onecom manages more than over 325,000 mobile connections, delivering communication services and unified solutions across fixed line voice, connectivity and cloud computing to some of the UK's most dynamic companies. It is currently Vodafone UK's largest partner.