What you can do is get an account at a place like callcentric which allows you to setup rules such as simultaneous ring.

And you can use https://sip.cheogram.com/ to get a SIP address you can put into callcentric to forward to.

But there are a few wrinkles:

First, Callcentric has a bug that doesn't allow percent in the fields. That sucks and means that we can't do the easy thing at the top of the page linked above. So instead if you type your Jabber ID into the box on that page it will give you a number that starts with "*10816". Everything after that @sip.cheogram.com is what you want to tell callcentric. For example, I type "test" in the box and it gives me "*1081686718586", so I want to tell callcentric "86718586@sip.cheogram.com"

So that will allow Callcentric to ring your Jabber ID.

The other wrinkle is that callcentric (and every other sip provider) can't call the JMP.chat SIP accounts. So you can't forward to that, but honestly you don't have to because callcentric gives you a SIP account and you can just use that one instead of ours.

Then when you've got that setup, you should be able to set our system to call callcentric, and then the calling rules will activate and do the thing you want.

Is not accepting a percent sign a bug or a feature. Many apps refuse percent sign as it is used for malicious code insertion.