Welcomm Communications, of Market Harborough, has bought Crown Mobile Communications, in Coventry, and CDM Global Communications, in Nuneaton, for undisclosed sums.
It means five staff have joined the Welcomm team, taking its workforce to 47.
Welcomm now manages some 40,000 small and medium-sized business customers for the O2 mobile phone network in and around the Midlands.
Between them the acquisitions have added more than 5,000 O2 contracts to Welcomm's books – 3,000 in the Crown deal, which was completed last month.
Welcomm has now bought out three businesses in the past 18 months, after taking over Northampton dealer Dialect, in November 2009, which added 5,000 numbers to its books.
Managing director Aidan Piper said the company hoped to complete at least two and up to four more acquisitions this year.
He said Welcomm had been able to expand because of its strong balance sheet. A lot of similar businesses, he said, had struggled in the past few years.
"We've been able to do this without having to borrow money," Mr Piper said.
"Crown was suffering with cashflow problems and so was CDM. We have bought the assets and the biggest assets of both were the contracts."
The company will keep hold of Crown's staff and premises which will be re-branded Welcomm Communications.
There have been no redundancies and the staff based in Coventry have already received additional training.
Welcomm founder and chairman Chris Stanton said he was delighted with the purchase and wanted to assure ex-Crown customers of uninterrupted service to their existing mobile contracts.
Welcomm was established in 1987 and in the past 18 months has seen its customer base grow by 40 per cent as a result of growth, the recent acquisitions and a close working relationship with O2 and other telecomms suppliers.
The business is in the process of building a 7,000sq ft head office close to its current location at The Point in Market Harborough to cope with the expansion.
Welcomm did not acquire the assets for a Crown office in Worcester, which is expected to close.