Raspberry Pi as wireless AP, with pluggable usb modem

[Mayuresh <mayuresh%acm.org@localhost>]

Is it possible to set up RPI (3B) as a WiFi AP and use a USB device (a
modem or USB tethered phone) to connect to the internet?

A different USB device may be used at different times, so the interface
may vary (or may sometimes be absent). Ideally it should not require
manually running a command depending on the device plugged.

If feasible, please help with more pointers or information.

-- 
Mayuresh