Check Free Interface when sending SMS over Multiple Interfaces

I have a RB953 actual with two Huawei ME909 Interfaces.
In cmd we can send SMS Messages over both Interfaces.
My Question
Is it possible to check if an Interface is in use?
If so the RB has to use the other.
We only want to say via API : RB send “message” to “Number” and the RB check which Interface is free