Help! Roaming in Chicago Transit Tunnels no Longer Works for Sprint

[jminor]

HELP. My phone will not work when roaming. The symbol is visible, good signal, but I get message "LB2 80". I found a thread that may help someone understand what may(?) be happening. Sorry for the long post, but I'm trying to give as much info as possible.
"Yes, we used to have roaming on US Cellular in the Blue Line tunnels (voice + 1x data). Yes, it stopped working a few days after VZW turned on its service in September. Yes, the phone shows there's a signal but you get the LB280 message if you dial. SMS and data don't work anymore either.

The current PRLs will make your phone roam onto USC in preference to roaming onto VZW. So it will lock onto the USC signal and not use the VZW signal. But when you try to make a call, it appears that USC isn't allowing it to be connected from the subway system. Oddly enough, when the train comes out of the tunnel, my phone will stay roamed onto USC for quite a while and I can make calls on USC above ground, but no t below. It's the same USC SID, but it won't connect below ground and it will connect above ground.

I don't think the VZW signal makes a difference because VZW is a lower priority in the PRL than USC in Chicago. A Sprint phone shouldn't roam onto VZW unless the USC signal is dead.

My suspicion is that when VZW got into the subway, somebody at USC looked at it and decided that they're paying the CTA money to have their antennas in the subways and that Sprint could install its own antennas if it wanted service. I suspect USC has deliberately decided to disallow roaming on the underground systems, probably with the exception of 911 calls (I hope).

FWIW, I have an old Ampd phone on PagePlus (a VZW MVNO) and it works in the subway on VZW.
Do any of the Guru's here have any idea how to combat this issue. Thanks for the great job.