Hello,
I have many clients is using ring central is phone provider. However, their service is high. Therefore, I suggest you with 02 options as below.
1. Option 1: you can still using ringcentral is your main service. I will help you to setup and organize everything.
2. Option 2: You hire a VPS with 10$ + hire phone provider ( ringcentral, flowroute, twilio,.. ) as your phone provider service ( fee about 0.0098$ / min ). System very stable and keep you saving a lot of money for the service.
The system will running with asterisk on CentOS ( latest version ). I can guarantee the system run very smoothly.
Please let me know if you have any question. I can give you some useful advise with no of charge.
Regards,
Vu Le