SpinVox operates a service that lets customers receive voicemail messages as SMS texts that can be read at their leisure instead of having to listen to every one.
However, the BBC said it had evidence that the conversion process is actually carried out by SpinVox employees operating from call centres located in countries such as South Africa and The Philippines.
The report went on to say that sending data outside the European Union might fall foul of European privacy regulations, especially if the company does not make it clear to customers that their messages might be listened to by employees.
SpinVox denied that the majority of messages are processed in this way.
"SpinVox has delivered world-leading breakthroughs in speech recognition and related technologies, developed by its Cambridge-based Advanced Speech Group," the company stated in its response.
"In the past two years, the Cambridge ASG team has applied the latest research to create state-of-the-art techniques that deliver a system that outperforms any equivalent speech technologies on accuracy, speed, scale, reliability and language range."
But SpinVox conceded that some human intervention is necessary, in order to increase the accuracy of its Voice Message Conversion System (VMCS).
"One of the key technology breakthroughs applied within VMCS enables it to 'know what it doesn't know'. VMCS can then refer a message to a human for assistance as required," SpinVox said.
However, the company did not specify what proportion of calls are referred to a human operator in this way.
SpinVox stated that it is fully compliant with the UK Data Protection Act, and that this permits it to process data outside the European Economic Area in compliance with certain requirements.
SpinVox also said in its response that its customer base is predominantly in Latin America, Asia Pacific, North America and southern Europe, and that it has no network operator services in the UK.
The company announced earlier this year that it had switched from targeting individual customers directly to selling its service to network operators instead.
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