I have a few questions about using a cell card with a Routerboard. For the cards supported by RouterOS, I'm going by the documentation page here: https://wiki.mikrotik.com/wiki/Manual:Peripherals
Currently, I have MC7700 and MC7355 modules, which have a mini PCI-e form factor, but use USB as their interface. I've already upgraded the RBM11G to the latest version of RouterOS, 6.40.3. Both of the cards have had their firmware flashed to the latest version on a Windows machine with a PCI-e to USB adapter; version 3.05.29.03 for the MC7700 and version 5.05.58 for the MC7355.
I checked that the cards were recognized by the Routerboard by running /system resource usb print and got something like this: According to the documentation, the best way to access a cell card is via the LTE interface, which doesn't show up for either card, which I guess means I have to use PPP. My questions are as follows:

• Is it as straightforward as creating a PPP client bound to the usb2 port, or is there more I should know about?
  When I contact AT&T to provision this card, are they going to know what to do when I ask them for PPP credentials or will they think I'm a nut?
  Is there any way to send AT commands to the modem?
  When it says on the manual page "Note that using PPP emulation mode you will not get the same max speeds as using the native lte interface." how much slower do they mean?
  Is there another card that would be better for AT&T, Verizon, or Sprint that isn't insanely expensive or hard to find in the US? I only pay around $20-$40 for the Sierra cards.

please make a support output file and send it to support@mikrotik.com we will check why the interface isn't recognized as lte.