Default [Q] SPH-L720 SlimROM with T-Mobile issue

I have been scouring the site and flipping back and forth between ROMS. I am having a common issue that is probably a modem configuration issue.

My setup:
baseband: L720VPUFNAE
kernel: 3.4.0-cyangenmod-gb508aa0
slim version: Slim-4.4.2.build.5-OFFICIAL-4050
provider: T-Mobile (prepaid)

Everything seems to work great except for two issue (maybe related):
1. I can't receive calls. Will go to voice mail after so many rings
2. I can't seem to initiate a hangup. It sits at "hanging up"

I have seen people in the forums with similar issues, but I can't seem to find an answer.

How can I access the modem configuration menu, "Service Menu"? Each time ai use *#0011# or the variants, I get "Connection problem or invalid MMI code."

if I go back to the sprint stock rom, I can send/receive calls, but lack data services. I really prefer to stick with the slim-rom. Pretty slick interface.

Thanks in advance, this is my first post.
-Robert