B2B dealer Olive Communications said it is to sue T-Mobile for £800,000 in lost revenue and £640,000 in unpaid commission following the termination of its dealer code last month.
Olive is looking to churn 50 per cent of its T-Mobile customer base to rival networks. It has 25,000 T-Mobile customers.
Managing director Mark Geraghty (pictured) said: "We connected on average more than a thousand customers per month on T-Mobile every month, and T-Mobile have historically struggled with B2B connections in the past so I find it all very hard to believe.
"It’s about rebuilding again, we have more than 10,000 customers on other networks and within 18 months I think we will have at least 25,000."
T-Mobile refused to comment on the Olive situation.
Olive said 250 of its largest business customers had already pledged to stay with Olive.
Olive is a gold partner with Vodafone service provider Yes Telecom and expects a "large chunk" of its customer base to move to Vodafone.
It is also connecting Orange and O2 indirectly.