I read the documentation but I'm not sure if the following configuration is possible with smsd.

I'd like to send some SMS with GSM1,GSM2, some others with GSM3, GSM4 and so on.
And I'd like to balance the number of SMS between the GSM.
So if I send 100 SMS through GSM1,GSM2 I'd like something like 50 SMS on GSM1 and 50 SMS on GSM2.

How can I edit the smsd.conf to reflect this configuration ?