running voip on third party server wtthout third party voip service

[CWR]

i thought *9 was a 3cx function. But maybe yealink uses same.
I wouldn't use any provider. I would find one you are comfortable with for your calls. Don't get stuck in a contract or cancellation fee.
I have used voip.ms and can recommend. Their support has been good to me this far.
With them you set up sub accounts for each extension. Those credentials are what you put into each phone. They have a ton of features. For like $2 month you get 3500 incoming minutes.
Try the providers out before you port your number to them.