All this is is a fancy earpiece (Score 1)

All this appears to be is a fancy earpiece. So, you could indeed use it to listen to a separate mobile phone, but before I implanted anything like this, I'd want to make sure it had a good security - lots of potential issues - to start with :

• do you really wanted to be bombarded by adverts EVRYWHERE you go
• whats to stop someone jamming or invisably replacing the signal
• they say no-one else can listen in - not to the sound, but what about the radio signal ?

All things considered, a pretty sketchy story - not enough detail.