In VoIP systems, ringback tone (the ringing tone you hear in your ear when you make a call) may be sourced by the local handset making the call, or by the destination VoIP device generating the tone and sending it as media over the VoIP link for the calling party to hear. When peering with Thinktel's VoIP network, either our switch or the remote gateway needs to generate ring back in order to hear it properly; not both. Contact the Thinktel Technical Support Team if you hear no ringback.