A first communication device sends a call request to a second communication device. The call request comprises a source address associated with the first device and a destination address associated with the second communication device. A communication system modifies the call request by replacing or augmenting the source address with a dynamic address and adding a key associated with the source address. The modified request is sent to the second device.If a user at the second device wants to make a return call, a call request is sent using the dynamic address as the destination address along with the key. The call request is routed to the first communication address by determining the source address of the first communication device from the key.