Faced with the problem of choosing a 3G (4LTE) modem?

Question

mobile connection

Dear inhabitants of this resource-paradise!
I don’t have any idea whether this post is on topic or not,
but I have to ask -
Several people are on fire with the idea of ​​​​creating a device that
meets the needs of our being ...
In terms of meaning and structure, everything should be assembled on the basis of a
3G USB-Modem, which looks like a flash drive.
Do not change the hardware, but change the firmware functions in it.
For more than six months, all manufacturers and suppliers have been playing football with us.
Hurt!
In principle, you can understand them, property, but you also need to understand us ...
We are exclusively a radio experiment ... The idea, damn it ...
In short, we need -
1. chipset
2. Firmware - including source code
3. development tools
4. OEM SDK
and —
5. possibility to upload user code
6. programmers manual if possible
No matter which model.
We decided this way - from the beginning there will be everything from this list,
and only after that it will look for and purchase a modem model for tests according to the info and tools found ...
Gentlemen!
Please help...
Best regards,