detecting modems on USB

the primary configuration of a modem is the device,
now with USB, it can be by chance whether the kernel attaches your modem to ttyUSB0 or ttyUSB1...or what if you have many modems,
and you want to be specific about which modem is where because you have them registered with different operators.
Anyone thought about this?
I think perhaps a id config needed in 
group = smsc
smsc = at

the id, maybe on AT+CIMI, or serial no, or somehow specified to be any or or of these.....