VoIP with t-home internet

I'm glad to see that I'm not alone here. My wife blames ME for trying to save us over $2K a year by moving from COMCAST to T-MOBILE business internet.

That’s right BUSINESS INTERNET.

I *NEED* to use a cordless phone system, connected to the internet to take orders for food, but my MagicJack system (which, BTW, I have used at home previously and have NEVER had a problem with, has an issue with our T-MOBILE 5G Router (the black tower one).  We have NO access to the SIP ALG on this Router.  I did everything I could to make this work; 

• changed power supply for the MJ device.
• connected the MJ device DIRECTLY to the router (there are 2 Ethernet jacks; one goes to my 8:1 switch, the other connects to a VOICE device. Everything ELSE works GREAT!

So my question is:

Has ANYONE had any success using a separate router, directly connected to the TMOBILE router, to use Magic Jack?

I would purchase a land line, but NOBODY offers a land line anymore. They are ALL VOIP/Internet solutions.  That means that I don't expect much greater success using other VOIP services (e.g. Ooma).

It is ODD that T-Mobile wouldn't FIX this issue, but maybe it's just me. I'm an MSEE and presume that access to those settings is NOT a big issue, and if it fixes the problem, they would likely make lots of friends. HELL, if I was a consultant to T-Mobile, I'd TELL THEM TO OFFER A VOIP SERVICE for $10/month and I'd bet they'd make BANK!

ANY suggestions/experience would be appreciated.  I do not want to go back to COMCAST. I am happy to make a one time hardware purchase for long-term service cost savings, but I *NEED* to have a working phone SOON, or I will be pressured to pay COMCAST their blood money...