I've been playing with this off and on for the past month+, and I'm nowhere closer to success. The device I started out with (0x1199/0x901e) was not recognized by pfSense, nor Centos 7. Windows 7 was no better – 0x901e is not a popular variant of this card, and no matter what drivers I used (starting with Sierra Wireless, progressing to shady 3rd party 'driver manager' sites, and even modifying inf files of the official SW drivers), I ended up with the card not actually working. Plus, at no point was there a working serial port provided to any of the OSes, so even if I wanted to issue AT commands to change PIDs, I was SOL. Because this device was an AliExpress import of questionable origin, I figured I should cut my losses and find another EM7355.
Next step: I obtained a less "exotic" variant of the card, a Lenovo part (FRU04X6038) which gave me 0x1199/0x901f. No better under pfSense (now at 2.3.1_1) or Centos (neither picked it up in a way which I could talk to it, serial or otherwise), though under Windows (10) the drivers obtained from Sierra Wireless picked up the card without having to modify any inf files. Still, the COM ports it did present didn't actually respond to any commands (trying multiple speeds, etc.) nor did the Sierra Wireless Watcher software pick up the card. I next tried it in a Lenovo laptop (Win 7) in which the card was supposedly compatible. The first time around, the laptop booted up, I installed Lenovo's drivers, and things seemed like they were going in the right direction. However, upon a required reboot (Lenovo Access Connection software), the laptop refused to boot due to what it claimed was an incompatible card. No idea why it was okay with it at first, but now it was complaining. VID/PID seemed to be the same.
So, I'm pulling my hair out here! I'd be hugely grateful if someone had some experience with these cards and could give me some pointers on where to turn next. Sierra Wireless doesn't seem to pay attention to end-users.
Ultimately, I'm looking for a T-Mobile (USA, LTE bands 2 and 4) compatible device which I can connect to my pfSense box, either via Mini PCI Express or USB. I don't want to spend hundreds on a Cradlepoint (or similar) box -- I'd be paying for a router (which I'd rather be pfSense) when all I need is an interface to a modem. If you know of a device that would accomplish this, hopefully under $100, I'd throw these EM7355's out the window in a heartbeat.