If you are forwarding calls to a mobile number then you may experience ring delays.  These are normally an issue related to the time that the mobile network takes to locate the handset across the mobile network via its local transmitter, and are part of the nature of mobile phone networks.

You will find that the time that it takes to connect to a mobile phone varies, depending on things like weather conditions, we infill this time with a “ring ring” tone, to avoid the gap that the caller would otherwise hear.

Whenever you answer calls via VoIP on your mobile device, you will notice that the connection/ ring time is much shorter.