When a call reaches the cellphone, and is routed via Genesys Cloud, we identify the following use classes
Reject with native IOS/Android dialog In this case, on PSTN level you're redirecting the call to the voicemail. The app doesn't come into play in this scenario - and from Genesys Cloud perspective, it looks like someone answered the call. Unfortunately, for this use case there is no solution: the app cannot intervene here (unless you would use scenario 2, where you click on the reject button in the app), unless you would manage to change your phone settings in terms of what happens when you click that 'refuse' button. (Based upon our investigations, we did not manage to find an option allowing us to change the behaviour - we could only change voicemail delays for scenario 3)
Reject using the reject button in the mobile app This is actually the only case of the 3 scenarios where the app comes into play - for the 2 others, there is no communication with the app, only between Genesys Cloud, your PSTN provider, and your mobile phone. When this button is clicked, via the Genesys Cloud platform API, a reject is issued. This allows routing on Genesys Cloud side to react (send to voicemail, or route to another target)
No response within x seconds from the user Here it depends on the voicemail settings in Genesys Cloud vs your mobile phone. In Genesys Cloud, on the level of your person object (see below), there's the option Timeout seconds. admin > people > phone For the scenario in which the user does not respond in time, you should ensure that the value on Genesys Cloud is configured to a lower value then on your cellphone (for example: if your cellphone's settings state to redirect after 30 seconds to your PSTN provider's voicemail, the value on Genesys Cloud should be set lower then 30 seconds).