Wireless Infrastructure Group (WIG) has agreed to take on board a new shareholder.
Venture capital firm 3i Infrastructure has committed £75m to take a 25% stake in the Bellshill-based firm.
The company builds and operates telecom masts in suburban and rural areas.
Being independent of the major mobile phone operators, it provides capacity which they can pay to share.
Earlier this year, Bellshill-based WIG announced plans to invest £1bn in new UK infrastructure.
That is to be focussed on new, mainly rural locations for masts, as the telecoms regulator requires providers to reduce the 'not-spots' in coverage.
The expansion includes installation of small cells and fibre-optic wiring to boost mobile connections in big buildings and on city streets.
The company also plans to expand in meeting mobile communications demand from rail passengers.
WIG was founded 10 years ago, and now operates 2,000 masts. It has expanded into Ireland and the Netherlands, and plans to expand further into western Europe.
The investment by 3i Infrastructure adds to the shareholding by US-based Wood Creek Capital Management, and the Lanarkshire management team.
Scott Coates, chief executive of WIG, said: "Bringing an established European infrastructure investor on board, alongside our existing North American partner, provides us with the financial capabilities needed to scale up our business through investment in up to £1bn of new infrastructure.
"This will transform our ability to support our customers as they extend network coverage in rural areas and improve capacity in urban centres.
"Independent infrastructure companies like WIG provide a conduit for long term infrastructure investors to support the telecoms industry as it takes on the challenges of expanding the quality and reach of connectivity."
A Lanarkshire mobile telecom firm has secured new investment which values the whole company at £300m and opens up funding for a major expansion plan.