Firstly, thank you for taking the time to post your concern to the Xfinity Mobile Forum. Secondly, my apologies for the delay in responding. Know that our team is growing, and our response time is improving.
Regarding your question, all phones on the network are automatically programmed to send incoming calls to voicemail approximately 30 seconds after receiving the call. Depending on the ring tone for your device or the ring tone assigned to the caller, the number of rings may range from 4-8 before sending the call to voicemail. Please keep in mind that these settings cannot be altered.
Hope this helps.
My mobile phone - Moto 5 - does not keep ringing for 30 seconds!
If it (like an iPhone) is supposed to ring for 30 seconds, this needs fixing.