Operating system name and version: Debian guest container @ Proxmox 3.4
Version of smsd: 3.X
Smsd installed from: sources
Name and model of a modem / phone: 12d1:1001
Interface: USB

I am lookig for a solution to force SMSTools to send SMS via certain GSM
For example:
I now have a VM with 4 sim cards in Huawei modems, lets call them GSM[1,2,3,4]
And i would want at least to know if its possible to send sms with 1 script via GSM[1,2,3] and with another via GSM4.
If it's not possible i can always clone the machine and use 1 gsm in 2nd guest system but I want to do that only if there is nothing else i can do.

You can use queues. For example see this post. Also read about Configuring providers which is the same thing.