B2B dealer Olive Communications is demanding more than £1.2 million from T-Mobile in owed commissions and compensation after settlement talks broke down last week.
T-Mobile sacked Olive in June 2008 for sub dealing with a black-listed company; an allegation Olive refutes.
Olive claims it is still owed £400,000 in unpaid commission and is entitled to more than £800,000 in lost earnings.
Olive boss Mark Geraghty (pictured) said Olive is churning 500 T-Mobile customers each month to rival networks.
Geraghty said: “We have tried and failed to reach an agreement with T-Mobile. We will now file our claim.”