Thank you so much for your support, it wasn't necessary to call to Plantronics, but I appreciate your help spec! I know the headset isn't expensive, but is something I had laying around my house and wanted to repair it, since the only problem was the cable. I had another one, but I would be satisfied If I could repair those phones.
Thank you for the support, I've ordered jack replacements from eBay, as soon as they arrive I'll post the verdict.
Best regards,
João Dias